text:
SMS Thread / General Limit?
Is there a limit within Android, or possibly set by OEMs (heard this from a friend who is a technician), of the total amount of SMS messages you can have? As in, messages within a thread  and/or all threads combined? Not just the limit within conversations which you can manually set. I mean a limit android has coded into it, or one that OEMs set, that actually would "limit" (whether by slowing down or stopping) the number of SMS you can have?
And I'm not talking about a couple thousand, but even in the hundreds of thousands in a thread?

I cannot provide a definitive answer, but some folks have had over 20,000 messages, based on this Reddit discussion. So if there are any limits, it may have been set by the OEM (or their custom app). Using 3rd-party SMS apps might provide a workaround to the limit.
I would bet that if are hundreds of thousands of messages, there could be a significant performance issue, although that may depend on how the app processes the records. Go SMS Pro, for example, does not load the messages all at once. But if it reaches the point where it has loaded already a lot of messages, the app slows down.
UPDATE #1: To paraphrase Izzy, the storage limit will also trigger the "insufficient memory" error, usually when there's less than ~25 MB free space on internal storage. This would also prevent the SMS from being stored (plus the possibility to send some on your own).

Well, I have ALMOST 100,000 SMS in one thread. I currently use Hangouts with the new SMS integration, but previously had to use GoSMS. GoSMS would be a little sluggish, and annoying. But, in the stock SMS app, I could load it one time, tap the big thread, and it wouldn't load. Then when I went back to the thread view, it wouldn't load. I don't want to delete them, and I won't. Just wondering why that happens, and if there is a limit in Android/OEMs.
Also: I am rooted running a CM 10.1.

@David I would assume this would be more of a hardware issue. On a PC, just try opening a really large text file (maybe 2-5GB) on Notepad, on an average PC. I think it would crash.

I thought of that as well. Is there an app, that you know of, that would, cache x amount of the messages, only loading them if specifically called upon? Like if I kept scrolling up in the conversation, and hit a "load more" option? That seems like a simple enough fix for large SMS threads, no?

@David I have no idea. You'd have to check the play store for that. 100K seems overkill to me though. I normally delete my conversations after some time, or back-up those that are important to me.

well yeah I could always backup and store somewhere. But I haven't found a solution for that which I like, yet. I just think, that even how absurd the message count is, the app should be able to handle it. Every message already sent or received won't change, so there is no need to load the first x amount of messages after a thread hits x length.

One more thing to keep in mind (geff, you might wish to include that directly with your answer) is the storage limit triggering the "insufficient memory" error. If I remember correctly, that would also prevent SMS from being stored (plus the possibility to send some on your own). This error is triggered usually when there's less than ~25 MB free space on internal storage.

@Izzy no it isn't. It just REALLY lags the phone / stock SMS app. I have over 10 GB free on my internal SD card (no external slot). I never get the memory issue, just the lag.

@David I think the phone can only handle so much (think of PC RAM vs hard disk)

@David I didn't mean to say this has to be the reason in your case (and I'm sure geff didn't understand it that way either). We were just completing the list in general, as for a future visitor this might be the crucial point. And it could have been a point in your case, so we wanted to make sure you know it and eventually can either rule it out. Besides: the internal card is of no interest for it, neither is the external card. The insufficient memory error is only related to phone storage (aka "internal storage"), not to any SD/external storage.

@Izzy Oh okay. Just thought you might have meant that was happening to me. But do you think an SMS app, designed (probably on some simple function) to cache a certain number of messages and not load them, would alleviate my problems?

@David Sure, why not? [But ASE is not a programming site. That would be better off in StackOverflow]


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make to show Japanese language on android device
I install app which supports Japanese language. But in my phone, it didn't show the Japanese language. My phone is sony xperia z. How should I make to see Japanese language.
Thanks.

Japanese is included by default in your device. Did you check the language setting to make sure that the language is not available?

Yes. I did. There is no Japanese language in my device. There is only Japanese keyboard. when I typed with Japanese kb, it shows blank.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


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Can a wifi hot spot be set invisible to just one specific android device?
The wifi hotspot i usually connect to has suddenly become invisible to just my android phone but is visible to everyone else. Is this possible or is there something wrong with my phone?

It's possible to block a certain device from connecting to a Wi-Fi hotspot. Just not sure if the hotspot would be hidden for the blocked phone though.

that is the dilemma!..its not visible to me but is visible to everyone else and all the other wifi hotspots are visible to me except the one in question.

Maybe it's configured for a channel your device does not support? In certain areas, there are limitations concerning which channels are permitted by law; so there could be a kind of "enforcement" in action on your device.

@Izzy that could be it but i have been using the same wifi hotspot for quite some time now and just yesterday it went out of range. and i can connect to the same wifi hotspot from other devices plus all the other wifi hotspots are still visible and connectable on my phone.

Then check on those who are able to join which channel they are using. And where the device is able to connect, check as well to see if there's an overlap (which would rule this out again).

@Izzy any idea how do i find out which channel the wifi hotspot is using?i have tried a few apps namely wifi analyser and a few more but none tell the channel on which the wifi signal is being broadcasted.

@Izzy just found out that my wifi doesn't display any wifi hotspot that uses 5GHZ frequency..guess my phone doesn't support 5ghz frequency

my phone supports the following protocols: Wi-Fi 802.11 b/g/n, 2.4 GHz, dual-band, Wi-Fi Hotspot. so does dual-band means it supports 5Ghz as well?

Not necessarily, it seems: What Is a Dual Band Router? explains it like "two antennas", so you could use e.g. 802.11g and 802.11n simultaneously (and not necessarily at different frequencies). I'd say that rather gets interesting with the device's hotspot features, serving different clients at the same time. // as for the channel: Wifi Analyzer and WiEye show it both.

thanks for all the help..the wifi hot-spot has been shifted from 2.4Ghz to 5Ghz frequency  which is not supported by my phone and hence the hotspot isn't visible anymore. guess its time to buy a new phone.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Nexus 7 Kitkat update showing Verification Failed error
When I tried to update Nexus 7 to Kitkat from Settings > About > Update, it downloads the Kitkat update and after that shows "verification failed". I bought Nexus 7 from US and now I am in India.

Are you rooted? If so, have you changed any system files? Does the error give any more information, usually it will state which file it has failed verification on.

@bmdixon Not rooted

I had the same problem on my Nexus 4 - I got the "Verification Failed" message twice, and on the third try it worked.


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How can I set a data cap per application?
In Android, you can see how many data each application has used. You can also forbid an application from using data by hand. And you can set an automatic data cap for the entire system. But is there a way to automatically cap how much a certain application can use?
An example scenario is how Cyanogen (a custom ROM) kept trying to download Android updates from Google on 3G, over and over again, even though it couldn't do anything with them. It was of course not supposed to do that, but it did this for many users. It emptied my monthly bundle in a day. In the statistics, this data usage showed up under the Google Services Framework, if I recall correctly.
I did not want to block this application altogether, because much of the Google stuff depends on it. So I wanted it to be blocked from using any more data over a certain threshold. In the end, I disabled the receiver that queries for updates; but that was an emergency solution that shouldn't have been necessary.
I'd also like to be able to cap certain applications individually in the future, for who knows what might happen. I might want to cap my Internet radio in case I forget to turn it off, or whatever. I can't find an application that can do this; can you?

Well, I don't know of any application that can "cap" data usage, but there's a useful application called Android Firewall that can disable / enabled Wi-Fi and 3G/4G connection so you can use the application to disable Wi-Fi and 3G/4G connection for certain applications when these application do not need an Internet connection. You could also log a request to the developer of Android Firewall to have a capped feature in future release of this application.


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How to run a mouse on android 7.1 (TV Box)?
I got gifted a nice wireless mouse this morning.
I've seen android work with a mouse before so I figured it can handle it as a plug an play, given that this one doesn't have fancy buttons that can be configured - hence needing special software.
Well that wasn't the case, and the manufacturer of the mouse doesn't have android drivers.
Is there such a thing as a general mouse driver I could find. If windows while offline can give basic functions to a new mouse, can we give a helping hand to android to jump the gap?
Normally I'd just go to the store and swap it for a Bluetooth mouse but its a friendly gift and I don't want to do that unless i have to.
The tech is "96 pro plus" tv box (has two usb ports) runs a cable mouse with no problem.
(Just returned it and got a bluetooth replacement in the end)

please provide more information. are you talking about amazon fire tv stick? Is it a bluetooth mouse or a WiFi mouse with/without usb dongle?

h96 pro plus tv box (has a usb port) and wifi mouse. The mouse mouse is named in the fifth word of the original post come on  :)

according to the specification the H96 Pro Plus Smart TV Box has USB-OTG support. just plug in the usb dongle which comes with your mouse

Did you seriously think that I didn't try and came asking for a driver before I even tried the mouse? It has enough usb capability to use a thumb drive, but apparently not enough for a mouse.

you would not believe what questions asked here daily. for android there are no such things like drivers (not at consumer level, at least). Newer android devices usually come with usb-otg support. for mobiles a usb-otg adapter is required. the adapter requests the device to interact in host mode (by short-circuiting pins 4+5). Assuming your Smart TV Box already has this inside, no adapter is required in your case. Try cable mouse instead for testing purposes

A cable mouse is working fine.

please check if the WiFi mouse is working on PC. Maybe there is a switch you missed, or batteries are empty. There is nothing you can do from android side. for mobiles there is sometimes external power supply required, which should not the case for TV box (for mobiles use this charging hub: https://www.amazon.com/dp/B07JZND95Z )

I did, before posting the thread. Its was operational on pc. I guess im trading it in for a Bluetooth one after all. Still the box was worth the money. I would have spent 5 times that for a smart tv that would have been dumber in the end.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
SSH tunnel with two hops
I would like to build an ssh tunnel from my android device (call it A) on port MMM to a machine C on port NNN.  HOWEVER, A and C are not directly connected.  They are only connected through machine B (which is also running an ssh server).  Finally, port NNN is only open locally on machine C (which is also running an ssh server).
So, with openssh in unix, I can use the command line of ssh or the ProxyCommand argument in .ssh/config to archive this:
Host C-tunnel
   HostName C
   Port 22
   Use username
   IdentityFile ~/.ssh/myidentityfileforC.pem
   ProxyCommand ssh -e none -i /.ssh/myidentityfileforB.pem username@B nc -w 120 %h %p 2> /dev/null

I can then set up a tunnel straight from my localhost to C:NNN (through the connection above).
Is there an app for android that supports similar?  I tried connectbot and ssh autotunnel.  The later got close, as I could set up one tunnel from A to B and then another from A to C (through the tunnelled A->B connection), but initiating the latter brought both of them down.  Setting up just the first tunnel and then using connectbot allows me to connect via ssh to C, but I cannot set up a port forward directly to C:NNN.
Any suggestions?  Is there a direct port of openssh I've missed?

Perhaps this is totally wrong, but could you use a virtual machine on machine B and create a tunnel from there to A?

Were I in control of machine B, that might be possible.  However, I cannot open ports on machine B (or if I did, they wouldn't be accessible).  Thanks.

Oh, I see. Well, good luck! Perhaps someone more knowledgeable will come by.

I would like to share info that JuiceSSH has the feature you're trying to achieve with just one click. I'm talking about its feature "connect 'via' other SSH connections." Even local port forwarding from the second server thru the first ssh connection works too.

Outside of stackexchange, I also asked some colleagues.  One suggestion they had did work.  In particular, instead of using ssh autotunnel for the tunnels, I used connectbot to connect and create tunnels.  They can be layered.  The only downside is that I leave a shell open.
More specifically:

I use connectbot to connect to B (ssh, port 22) and then add a forwarding
from a port 2222 on A to port 22 on C.  I leave this shell open.
Then I make a new different connection to port 2222 on A (which opens a shell on C) and add port forwarding from port 2NNN to "localhost:NNN" (which is actually C:NNN).

Now I can connect to A:2NNN (my localhost, port 2NNN) and get to C:NNN as if it were local.  I have to leave the shells open, but it works well enough.

This is based on shelton's comments but they confused me, so here's how to do a "-J" hop using ConnectBot, e.g. via something like serveo:

Add a connection to the Hop host (e.g serveo). This is purely a "man in the middle", and will be used to forward to the real host. E.g: "user@serveo.net". You can turn off "Start shell session".

Save the serveo connection.
"Hold" the serveo connection in your list of hosts, and choose edit port forwards.
Add a new port forward. Type: "Local", source port: "2222", destination "alias:22". This opens localhost:2222 when this serveo connection is made, which will forward/hop your connection to the target host.

Add a new host, matching the port forward. E.g "user@localhost:2222".

The normal usage workflow will now be:

Connect to the serveo host. This will start the tunnel. Close (but don't disconnect), so the tunnel stays active.
Connect to the second (localhost:2222) host. This will run through the tunnel to your remote host. Authenticate as normal and voila!

Thanks.  I did end up using connectbot as you suggested.  The need to "click twice" is annoying, but it certainly works.

Ah I just realised your answer was actually to your own question! I ended up fighting this a bit, your answer helped get 90% of this running but the last parts confused me a bit, so thought add an answer in case anyone else stumbles across the same confusion.

It's a bit annoying, but super cool that this works from my phone. Can trigger some automation while on the move now, easy peasy :)

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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What is Maximum recording video size?
i would like to use my smartphone to record my team soccer match.
I've two question, one of those, a little off topics.

Our match length is 60 minutes. Do Android allows a 720p recording of 60 minutes ?
Is it possible to turn off display when recording ?
(a little off topic) I need a good solutions to 'append' my smartphone to a 'rounded' coverage (see photo).. i've tried to use tripod or 'car holder' ...but neither is a good solution.
Have you got some ideas ?


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Ubuntu for Android
Is this actually downloadable in Google Play or elsewhere or is it just a project for willing OEMs?
Did anyone here use it?
http://www.ubuntu.com/phone/ubuntu-for-android

@krsteeve You're talking about Ubuntu Touch. Mr. Brehm is asking about "Ubuntu for Android", which is listed as a separate project on the site he links to.

I'm pretty sure it's only for OEMs at this point. The developers did a Q&A on Reddit a few months back where they basically stated they had no immediate plans to release UfA (see, e.g., this comment thread). Don't know if anything has changed since, but the lack of a "download" button would imply it has not.


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Contact synchronization on older droids
Having had the "activate auto-sync" checkmark off for about a week (not that i expected this time-out to matter in any case), i've recently tried to find a manually-driven option, but without success. My 2.3.4 Gingerbread (Level 10) doesn't even animate the curved arrows anymore. After giving up, i've even activated the auto-sync, but it still did not kick in. :-|
Then i tried to look into other options, and got to the Contacts app, where in the Menu there's an "Import" option, but this one fails to even start -- with a silly error message "Memory full. Could not import contacts." My internal storage still has 16 MB free, though, so i suspect it's the number of contacts that's causing the issue? So, anyway, how do i check what's wrong and is there any workaround for this SNAFU?

To answer a part of your issue: Have you checked our insufficient-memory tag-wiki? That error is triggered when your internal memory drops below ~25 MB, and could even affect the storage of an incoming (160-char) SMS, stupid as it might sound... Btw: first-aid is also available in the tag-wiki.

@Izzy : no, i didn't yet try any of those ideas since i haven't started considering the low internal space a problem... It's just a possible minor inconvenience when i want to install a new app. But do you really expect me to understand that "FULL" can actually mean "low space"?!?

@Izzy : on the other hand, i'm currently going through the effort of cataloguing (and backing up apks of) internal-storage-hungry apps, so maybe i should just be patient and try again after i finish that and decide which of them to uninstall?

As I wrote above, and the linked tag-wiki states: that error will always pop-up on low storage. So that is your underlying problem. The tag-wiki contains hints on how to deal with that; please check those out first. Afterwards, feel free to return with specific questions, of course, if there are any left :)


text:
Android lost some apps - how do I dl Whatsapp again?
My HTC Evo 4G piece of trash all of a sudden deleted some of my contacts and apps - including the app market (google play?).  How do I get Whatsapp back - which I paid for through paypal - if I can't access the market store?  Google play asks me to sign in with a gmail account - but I didn't use a gmail account when I bought the app so it doesn't show up when I sign in.

So you didn't use your GMail account to sign in, and payed using Paypal? For even one of the two, it cannot have been Google Play where you did that, as it required logging in with your GMail account long before the first version of WhatsApp became available. And they never accepted Paypal for payments. So you must have been in a different universe then.

You can pay for Whatsapp with PayPal on their own site, so it must have been from there.  You can download the app here...
http://www.whatsapp.com/android/
and, as it says on that page...

If you already paid for the service you will not be asked to pay for it again.

If you bought it with Paypal, it must not have been through the market.   Suggest you contact the developer for advice.


text:
Email won't stay deleted (IMAP)
Phone: Samsung Galaxy S4
App: default mail app (Android or Samsung, don't know which)
Issue: I have an IMAP email account and when I delete an email and then check for new messages later, or at the scheduled sync frequency, those emails reappear in the account - they won't stay deleted.
I can't use K-9 mail as it doesn't support Exchange Server and I have an Exchange account as well. The problem account is set up as IMAIL. I don't see any options anywhere to change server settings for deleting emails on the server as well. Any ideas?

Looks to me that the problem is with your IMAP server configuration...

I had lots of (similar) issues with the default mail app using my IMAP account, and was glad I was able to switch to K-9. Sorry to be of no further help.

IMAP settings are fine. I've removed the account, reset the phone added it again and no luck. If it wasn't for the need for Exchange support I'd move to K9 but it isn't an option sadly

In my opinion there is an issue with the default mail app on the Samsung Galaxy phones.
I have recently switched from iPhone to Galaxy Note 3 and was really disappointed with the mail app not properly deleting emails from the server using imap. I know what I am doing and have it successfully working on other DROID and ios devices.
My work - around is to not use the trash can icon to delete mail but instead to use the move icon and choose to move the mail to the INBOX.trash folder.
Or you could just use Maildroid as there is much more control over what you want to do.
I am back on the default mail app now and happy with my work - around as the samsung email app works best with the Galaxy Gear smart watch.

This might seem silly to ask, but is your auto-sync to gmail setting on? Assuming your email's IMAP settings are correct, then the issue is with your phone. In the case of the default email android client, you need to have auto-sync on for each added email account. Once that is checked on, your emails on the server will reflect any changes made on the phone.


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How is it possible that an app stores its data even though I clear the cache and uninstall?
I have downloaded an app (its a game), made some test progress, and then deleted the game data. I have also cleared the cache and uninstalled the game, but whenever I install it again from the Google Play Store, the progress is still there.
I have also tried installing the app after clearing its data, offline from the .apk-file.
How is it possible to retain the app data like this and how can I clear the data?

Since you mentioned you were still seeing it after installing offline, I'm going to assume you also tried the game while still offline. If the data was there, it could have made a folder to hold the data which you could get to and delete using a file explorer. There's a number of apps that make folders to hold data that don't get deleted when the app is uninstalled.

Yes, you might be on to something. How can I track down the files? :)

Install a file explorer this one should be fine. Then go in and look for folders that have names of the uninstalled apps and delete them.

It's possible that the game progress is saved in the cloud, if you are using Google Play Games.
The Google help page says you can clear this progress / data, but note that it will clear for ALL games:

If you want to delete your saved data from all games that use Cloud
  Save, visit the Google Settings app and select  Menu > Clear app data.
  This will clear all your data from all accounts.
Depending on your device, your Menu icon may look different.

Thanks! Is there a way to identify wether the app uses the cloud?

@subZero I don't know. :( There's this reddit thread, althought it doesn't help much: http://www.reddit.com/r/Android/comments/1ew5o2/which_games_have_supported_the_new_cloud_save/

I'm not entirely sure (as I don't use games), but the Google Settings app has an own section for this. It's empty for me (no games, as said), but looks like it should list games that have data stored to the cloud.


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Will Linux overwrite android?
This is properly a silly question but if I use Complete Linux Installer (https://play.google.com/store/apps/details?id=com.zpwebsites.linuxonandroid), will it overwrite my current system? And if it does, is there a way to dual boot it? Hope you can help me. Thanks!

From the description on the play store Complete Linux Installer is an all in one solution to installing Linux distros on your Android device. Brought to you by the LinuxonAndroid project the app is designed to allow you to install a full Linux distro without touching your Android install.

Looking at the description of the said app on the Google Play Store as referred by the OP:

Complete Linux Installer is an all in one solution to installing Linux distros on your Android device. Brought to you by the LinuxonAndroid project the app is designed to allow you to install a full Linux distro without touching your Android install.

So, it does not really "over-write" the Android installation. The emphasis in the above quote is mine.
It does pay to read the description on the Play Store thoroughly in order to avoid any confusions. If there is a confusion, the said developer would be delighted to receive an email asking for clarification as it shows that you as a customer is interested in the developer's app and might spur them on to improve it etc. :)


text:
Adobe flash for Asus Transformer TF700T
Does anyone know if the Adobe flash player will be available for Android devices any time soon? I have Android 4.0 Ice cream sandwich. On ASUS Transformer TF700T. I can watch movies, videos and only play some games that don't require Adobe. Someone, Anyone. Please Help!

See also: How can I use Flash Player now that it's no longer supported?

See also: Is Adobe Flash deprecated with regards to Android Devices and Apps?

There are several other related questions in the [tag:adobe-flash] tag.

Adobe Flash fot Android has been discontinued and all official methods of installing it have been removed. This is mainly due to problems in security, performance and stability, but the rise of HTML5 has also played its part. You can find more info from here or here.


text:
Why video made with iOS can't be read on Android but the inverse works
I'm currently testing why a video made with an iOS device does not seems to work on my Galaxy S3.
Here's the file info from ffmpeg :
Video took with Galaxy S3:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '20130715_151126.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 0
    compatible_brands: isom3gp4
    creation_time   : 2013-07-15 13:12:08
  Duration: 00:00:41.33, start: 0.000000, bitrate: 17143 kb/s
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 17015 kb/s, 30.01 fps, 30 tbr, 90k tbn, 180k tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : 2013-07-15 13:12:08
      handler_name    : VideoHandle
    Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, 123 kb/s (default)
    Metadata:
      creation_time   : 2013-07-15 13:12:08
      handler_name    : SoundHandle

Video took with iPhone 4S:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'trim.BE866F9A-654A-4C76-AC43-5CDF4923A2F0.mp4':
  Metadata:
    major_brand     : qt
    minor_version   : 0
    compatible_brands: qt
    creation_time   : 2013-11-15 12:44:22
    encoder         : 6.0
    encoder-fra     : 6.0
    date            : 2013-05-31T14:22:11+0200
    date-fra        : 2013-05-31T14:22:11+0200
    model           : iPhone 4S
    model-fra       : iPhone 4S
    make            : Apple
    make-fra        : Apple
  Duration: 00:00:21.79, start: 0.000000, bitrate: 4221 kb/s
    Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, mono, 62 kb/s (default)
    Metadata:
      creation_time   : 2013-11-15 12:44:22
      handler_name    : Core Media Data Handler
    Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720, 4147 kb/s, 29.97 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : 2013-11-15 12:44:22
      handler_name    : Core Media Data Handler

They seems to be fairly the same video and audio encoding using h264/aac
The only thing that differs I can see are :

The resolution (It should not be a problem)
The FPS (should not be a problem)
In iOS the audio is stream 0:0 while in Android it is 0:1

The thing is, a video took with a Galaxy S3 does work fine on iOS without recoding it.
Anyone knows why ?

Have you tried using a different video player?

I would like to use the default player, since it is to create an Cross-Platform App iOS - Android, I don't want to ask Android user to download another player in order to play it. And since video should be saved on the users gallery, I can't even do a Player myself... I would have to re-encode the video.

If you do not want your users to download a player to show the videos, then you have no other choice but to create videos with the H.264 Baseline profile. This is because the stock Android player does not support anything higher.
iOS on the other hand does support the Main and High profile. While not listed in the iOS specifications, the iPhone 4S and upwards should support it.
It could very well be that your Samsung's video app records High profile video and can also play it (because Samsung included a non-stock player*). In any case, converting to Baseline profile would ensure that the video is playable on all devices.
ffmpeg -i input.mp4 -c:v libx264 -profile:v baseline -pix_fmt yuv420p -crf 23 output.mp4

That should do it. You can change the CRF parameter to change quality. Check the x264 encoding guide for more.
* Disclaimer: I don't own a Samsung Android phone. No idea if they have a non-stock player.


text:
i wanna access the internet with my tablet via the second device
I got a tablet without wifi connection, and a device with a SIM card and internet access. I managed to get a Bluetooth connection between those two devices. Now i wanna access the internet with my tablet via the second device. Is there a way given through android to dial into the internet ? I thought about implicit Intents or Bluetooth tethering, but didnt find anything yet.
i hope u got what im asking about ;)
ty in advance

We can't help without knowing more about the device that has the internet connection, since it's the one that needs software to share the connection. What kind of device is it, and what software does it run?

Depends on the other device.
There must be an option for sharing the internet over bluetooth in other device's bluetooth connection settings.
If you turn it on, you can connect to internet on your android tablet.


text:
Android Icon keeps changing from what I set it to or disappearing entirely from the quick-launch bar at the bottom
I have a Galaxy S3 on Sprint, and the quick-launch icons at the bottom of the screen keep messing up.
I have 5 quick-launch icons there, but sometimes one of them either gets removed so only 4 show up, or it duplicates itself and overwrites another one. This leave 5 icons, two of which are the same thing. The icon I've noticed do this the most is ColorNote, but others will do it too.
1) What can I do to track down the cause of this anomaly?
2) How do I make it stop?
Anything you can do to point me in the right direction is much appreciated.

Is this using the default launcher, or a custom (3rd party) launcher installed from Google Play?

@geffchang This is using the latest version of the native one that shipped with the Galaxy S3. I think it's Samsung's addition to Android, but not sure.


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Tab bar in Chrome browser
I have a Galaxy S4. I use Chrome browser. Anytime I play with an Android tablet, Chrome has a tab bar like on a desktop OS. I want to enable this on my phone, but I can't find an option to enable it. I tried looking into the prefences file but didn't see anything pertaining to this. Is there a way to enable this? I'm rooted, and don't mind messing around so I don't mind if there's a "hackish" way to do this.
It seems like Chrome is a universal app, so I don't see why it acts different on a phone versus a tablet. Or at least provide an otion for it.

Yet to find a way for chrome without installing a tablet ui rom. Boat browser has this feature. After initial install it will dissapear if you scroll down the page. If you go to settings and lab, just tick the top option to show nav bar.
Dolphin browser also allows this but used too much battery and ran more sluggish to be worth it.
I dont understand why chrome doesnt allow it. Im on a note 1. Its a deal breaker browser feature for me.


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Charge Level Control
Would there be any application or method of controlling the charge level and limiting it for example to start charging at 20% and stop charging at 80% ?

why would you want to do that?

Lithium based batteries get better cycle usage if you don't use the full charge level.  If you normally use 50% then using 30-80% will give you more cycles then 50-100%. If you use the phone plugged in a lot (e.g. developing) then stopping the full 100% charge will help the battery life generally.  The long term life gets worse with charge level and temperature so fully charged and in use e.g. warm is a worst case state for battery life.

I've heard that about Lithium batteries, and I've also heard that it's an "old wives tale".  See http://android.stackexchange.com/questions/29073/battery-life-and-first-time-charging-on-li-ion-batteries-myth?newsletter=1&nlcode=36875%7c8c25.

The battery meter saying "100%" doesn't necessarily mean what it seems.  Check this article: http://phandroid.com/2010/12/25/your-smartphones-battery-gauge-is-lying-to-you-and-its-not-such-a-bad-thing/                   The signal indicator on a phone is similarly misleading, only worse.  The real reading is under about phone>status.

You can hardwire it: 12 ohms in serial still makes the phone be recognized by the computer, yet slowly discharge.

You could use Tasker to make a beep or push a notification when battery level is ouside your safety boundaries, so you can take an action by yourself (ie. un/plug the charger).
Go to developer website, where Tasker Userguide can help you to set that task, taking as context the State of your device.
The following image shows an example of configuring Tasker to take an action depending on battery state:

Application:
No, as for an application to do this, the answer is no since charging on an Android phone is done by its hardware! The software has nothing to do with the actual charging of the phone! (This is why your phone is able to charge even when the OS is powered down)
Method:
No, since the charging is not controlled by the software of your phone, this means it will be very difficult to stop your phone from charging (since there is no software modification that I can think of that will help... I could be wrong!)
However, as pointed out by Francisco Alvarado earlier you could create Tasker profiles to notify you about custom charge levels. Or if you are very paranoid about maintaining battery health you could make Tasker prompt you before automatically shutting down (just a suggestion).

Well one way of doing it would be with a device such as Raspberry Pi or similar (perhaps with java installed on it). With an add on such as Laika it can control devices including relays which could turn on/off the power to a charger. Since Android to PC communication is available over USB https://stackoverflow.com/questions/3803871/android-apps-communicating-with-a-device-plugged-in-the-usb-port then I'm guessing an app could talk to the fruity device, if not it could post to your own hosted web service. The app could then tell the device when to turn on the charger and when to turn it off according the the apps settings.
OK, a bit over the top and would need experimentation, but I think it could be done.
Lets hope that Android Marshmallow (or Maltesers or M&Ms or whatever it is) will have this built in for hardware that can support it.

It looks like RPi/Android USB communication is available, as it has been reported you can use this: http://android.serverbox.ch/?p=262


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transfer custom itinerary from Maps on PC to Android
I have a custom itinerary I prepared on maps.google.com on my PC (forcing some routing) and I would like to transfer it to my android smartphone, then use the navigation features of the Maps app.
The only thing I managed to do is to open this itinerary in a browser (on maps.google.com via the link I get on the PC) but not to transfer it to the Maps app. Is there a way to do this? Does the Maps app even supports custom routes?

Install Google Maps Engine.

Google Maps Engine on Android enables you to view your custom maps
  anywhere, anytime.

I'm not sure, but Navigation will probably not work as described here:

For navigation, searching for local places, etc. please check out the
  Google Maps for Mobile app.

I tried but I do not even know how to bring in my custom maps inside (it is bound to my account but does not see my maps, only a few public ones).


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Keyboard Macros
Is it possible to have keyboard macros? Like on iPhone if you type lol it automatically converts it into laugh out loud? Couldn't find it on my phone for multiple hours.

possible duplicate of How do I get quick access to common text snippets?

@AlEverett Quite a different scenario, but I suppose the answer could also be useful. Leaving this Open, just in case.


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Is there a way to cast video from one Android device to up to 2 other devices?
Lets say I have the following Android devices:

An Android smartphone running 4.1 with Wifi capabilities
(2) Android tables running 4.1 with similar Wifi capabilities

Is there an app that makes it possible to have the 2 tablets play a video file that is hosted on the smartphone?
The app or another app working along side it, would have to allow the devices to establish an ad-hoc wifi network.
The use case is that I would like to setup the tablets on the rear headrests inside my truck.  This way, the passenger can control the video being played to the 2 slaved tablets from a network-connected smartphone.  Are there apps out there that do that and if so, what are they?

Please note that recommendations like Is there an app for X are off-topic here (see our [help/on-topic] for details). You might wish to consult Where can I ask questions that aren't Android Enthusiast questions? to find a fitting place for your question.

Ugh. This question is fine. There is a well-defined problem to be solved. That an app is being asked for is secondary.

Thanks @Izzy, I followed your links.  The Help center suggests this question follows the guidelines.  It says "Using a particular app on your Android device" is ok. I don't see "Is there an app for X" anywhere in the discouraged section.

Having read it again, I agree with Al. Consider my comment as non-existing and never made ("Mu"); I'll still leave it there to keep the context to Al's comment (so we can learn from my mistake).


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SELinux temporary set to permissive
I am using a Galaxy s10+, rooted with magisk, no custom ROM, no custom kernel and no custom recovery. The rooting is heavily limited because of the SELinux enforce mode. Actually, no root command in termux works because of SELinux. I do not want to disable SELinux permanently for security reasons. What I want is something similar to the command "setenforce 0". This does not work on my phone however, and I think it could be KNOX related. It gives no errors but the output of "getenforce" is still enforced.
Is there a way to set SELinux to permissive mode only temporarily until next reboot on rooted Samsung galaxy s10+ with magisk, everything stock?
The linked duplicate is what i already tried, and it also says it does not work after 2015.

Possible duplicate of How to make SELinux permissive on a Knox Samsung device?

That is what i already tried as I said. The answer says that it no longer works after 2015.

Related: https://android.stackexchange.com/a/209374/218526

... and the answer remains the same after 2015: you need to run a custom kernel

@alecxs and OP insists on not having a custom kernel in 4 questions asked previously: 1, 2, 3, 4.

@Selinuxguy just built the kernel without SECURITY_SELINUX_ENFORCING=y. May be the source code needs to be patched.

CONFIG_SECURITY_SELINUX_DEVELOP=y

@alecxs yes, with that kernel starts in permissive mode, later enforced by init.

I almost literally did the same thing.. I went after an LG K30 Premier Pro and comes down to SElinux. I did mine to prove you can "Root" a phone without deactivating the bootloader. Still having hard time cause without deactive it either says your not rooted or it does say it and the phone inner programs send you an email and tell you they are going into hidding inside a FireStick
. pretry. Funny really. ..
Ok herwnis the email com.lge.software.cliptray
Version: null (0)
SD Maid
Version: 4.14.27 (41427)
Device
Fingerprint: lge/cv3_lao_com/cv3:8.1.0/OPM1.171019.026/19155140321d4:user/release-keys


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Galaxy Note 4 muffling external mics
I just got a refurbished Samsung Galaxy Note 4 to replace a dead Note II. When compared with the Note II, it is giving me terrible audio quality for voice recordings done with headset mics — there is a severe high-frequency roll‑off that leaves the recording sounding muffled.
I initially discovered this when using the headset that came with the Note II. I have a homemade windscreen rigged up on it, so I wanted to keep using it rather than trying to transfer that to the headset that came with the Note 4.
So, the exact same microphone and windscreen, using the stock Voice Recorder app on both phones, neither rooted, in high quality mode in both cases (recording MPEG-4 audio), and the difference is night and day when listening to existing recordings done on the Note II vs. tests on the Note 4. The recordings from the Note II certainly donʼt sound like a studio condenser mic (like in the appʼs graphic, lol), but theyʼre of reasonable quality, more than adequate for speech. High frequency detail is there; I can hear leaves rustling very crisply, and sibilants in speech are clear and distinct. The recordings from the Note 4, by contrast, sound muffled. Sibilants are muted and somewhat indistinct. It sounds like it was put through a low‑pass filter. Speech is still basically intelligible, but the gap in quality could well make the difference between making out certain words or not under less ideal conditions.
The overall signal level in the Note 4 recordings is also noticeably lower. I have to turn up those recordings more than the Note II recordings to compare them equally. (Iʼm wondering if that and the fidelity problem may be related — the MPEG codec might throw out very quiet high-frequency data by design.) I should note that in the Note 4 the “Recording volume” setting is set to “High” (thereʼs only that and “Low”).
Iʼm listening to both files on a PC with VLC media player, through a home hi‑fi system with proper speakers — not some cheezy self-powered made‑for‑computers garbage.
VLC is showing the recordings from both phones to have a content bitrate around 128kb/s, so I donʼt think itʼs a matter of bandwidth loss from more aggressive data compression.
I figured maybe the electrical parameters of the headset had changed between the two models, and so also did a test with the headset that came with the Note 4. It was maybe very slightly better due to the lack of the windscreen, but basically still horribly muffled — low signal level and significant loss of high frequency response.
I should note that this is not a problem with the Note 4ʼs internal mics. When I unplug the headset and record with the internal mic, the recording is much louder and has decent frequency response.
Possible explanations I can think of:

There has been a significant regression in the quality of the preamp or ADC circuitry for the external mic from the Note II to the Note 4.
My particular Note 4 has a problem in the audio connector that is introducing extra resistance. I have tried cleaning it with a cotton swab and isopropanol, and the issue remained.
My particular Note 4 has a damaged mic preamp or ADC circuit.
There is a system setting buried somewhere that I need to change, other than the obvious settings in Voice Recorder, which are already set to their highest levels.
There is a bug in the Note 4ʼs firmware.
There is a bug in the Note 4ʼs Voice Recorder app, but this seems unlikely, as I expect it just encodes whatever audio the OS gives it.

Any ideas which of these might be happening? If this is a problem in the model itself, surely someone else has encountered this long ago.
The exact model is SM-N910W8 running Android 6.0.1, kernel 3.10.40-8000148.
UPDATE:
I did testing with a 3rd party app that can record raw PCM into a RIFF (WAV) file, and the same muffled sound was there, so itʼs not the fault of the stock recording app or data compression.
Robertʼs suggestion led me to figure out that the ADC for the headset input is in a Qualcomm WCD9330 chip. I also discovered from schematics I was able to dig up that the internal mics are digital mics (the ADC is built into the mic), so the WCD9330ʼs ADCs are not being used for those. I also checked out the engineering specs for a couple similar chips in the same line (Qualcomm doesnʼt seem to have published specs for that exact device), and nothing there suggested that the frequency response should be anywhere near so poor unless the firmware has drastically misconfigured the chip.
I did find a reference, on XDA Developers here, regarding a totally different device, the Samsung Galaxy Tab S2 8.0 LTE, that uses the same chip and has muffled audio input caused by a firmware issue. In that case, a custom ROM was causing the issue, and the stock ROM worked fine. In my case, itʼs using the stock ROM (AFAIK!), but perhaps in this case the stock ROM is at fault.
I did some testing and found, somewhat surprisingly, that the frequency response is actually full hi‑fi with the exception of a two-octave 10dB notch at around 8kHz. This dip at 8kHz is very consistent with what the recordings are doing to speech. Given that the response is consistent with a notch filter, it now looks like the behaviour is probably half‑ways intentional, which was a bit mystifying. I decided to put up this question on the Electrical Engineering SE, to see if there might be a plausible engineering explanation.
The result of that discussion is that it would be normal, due to sampling rates used in telephony, to knock out frequencies above 4kHz in order to avoid transmitting severe aliasing artefacts to the remote party. That filter should get turned off when an app asks for PCM data at a higher sampling rate, but the electronics allows independent control over the filtering, so itʼs quite plausible that the firmware in this particular model, when disabling the filter for audio recording, forgets to disable it on the external mic input.
So far I have not found a confirmation of this as a known issue of this model, but it seems like the most likely explanation.
On a firmware/software level, Android devices are basically a black box to me, so I have no idea where in the software stack this issue would be most likely to be, whether this might be fixed by a custom ROM, or by some utility that runs rooted, or what.
Another dimension to the problem is the very low input volume level. I had originally thought that was related, though it now seems more likely it may be a separate issue. I did find the following suspicious lines in mixer_paths.xml:
<path name="rec-headset-mic">
<path name="ear-mic"/>
<ctl value="14" name="ADC2 Volume"/>
<ctl value="72" name="DEC5 Volume"/>
</path>

There are a number of other places there and in mixer_paths_i2s.xml (I2S is Inter‑IC Sound, a hardware bus used by the WCD93xx) that also set a similarly low number for the volume for ADC2.
I say this is suspicious because from what I understand, the integer setting here is in 1dB increments with 84 being 0dB. This would suggest that ADC2 is being set to -70dB — a remarkably low level! However, ADC2 is a hardware port whereas DEC5 is I think some kind of software mixing channel, so without much more intimate knowledge of Androidʼs audio hardware abstraction scheme, I canʼt be sure that the numbers for ADC2 are interpreted in the same way.
To make matters more confusing, there are two identical copies of this file, one in /etc and one in /system/etc. Also, the mixer_paths_wcd9330.xml file, mentioned for the Galaxy Tab S2, does not occur in either of these locations. And there doesnʼt even seem to be a /system/vendor/etc directory on this phone.
I canʼt edit this file to play around with it without rooting the phone, but Iʼm a little reluctant to do that, partly from having zero experience rooting phones, and also because if I do discover a hardware issue, I donʼt want the store to be able to blame it on that. So Iʼd need to first be confident itʼs going to fix the problem.

You could check the common web pages that present device tear-downs to get the info which chip is used for the audio/mic jacket and then check if it's recording quality is a known problem. Also check if there are reviews by authors / magazines with an audio background. May be they have written something that explains your observations.

@Robert  Most of the audio-type reviews I was able to find for phones tend to concentrate on playback rather than recording.  But the tear-down idea ended up leading to a bunch of clues, which I added above.  Thank you for the tips!


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Disable downloading system updates by default in Android
Yesterday got a notification on Nexus 4 saying system update available "Kit kat (Android 4.4)"
Have waited for the download to complete but showed a message "Verfication failed" and "Check Now" button at the button.
Clicked "Check Now" button and it started the download again, it happened a couple of times and really irritating that it tries to download update from the beginning every time.
Now, as not sure what's the problem, want to try updating to kitkat version after a couple of days and want to disable auto-download for now. Is there any way to disable auto-download of system updates or any one else faced this problem?

Have you rooted your phone or installed a custom recovery?

No. It came with Android 4.2 and upgraded to 4.3 earlier and haven't faced this issue.


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Locating My Files in Android 4.0.4
I have bought a new Android phone (Intel Yolo Smartphone) and it runs on Android 4.0.4. However I can't seem to locate the My files (It is called that way in Android 2.3.6) folder so as to access the internal memory storage files.
In Android 4.0.4 the folder is called by which name?

You can download ES File Explorer. It's a free file explorer for android.
Download from Google Play
It's quite easy to use and doesn't require root access.

Look for a folder named sdcard using a file explorer app.


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Prevent ANY sound from Android phone
I have the Galaxy S4 and would like to be able to ensure that, when on silent/vibrate mode, the phone makes absolutely no noise. I haven't been able to find a way to prevent the alarm from making noise when going off in silent mode, and though I could set the alarm type to vibrate, I'm concerned that if the alarm can go off in silent mode, other things can make noise as well.
Is there a way to ensure the phone makes no noise? Is it really only the alarm that makes noise in silent mode?

Check out Volume Control +. This app lets you control the volume for the following: Media, Ring, Notifications, In-call, alarm, system. Each sound profile (e.g. Silent, Vibrate, General) can be configured.


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Android - shell utility to perpetually disable headset device?
I have an HTC Desire HD device that has some schmutz in the wired headset jack, and the output from 'logcat' (http://pastebin.com/cNZC8Wwc) shows it vacillating between 'Headset=true' and 'Headset=false', when there is in fact nothing present in the headset port.
I/HeadsetService( 1977): Headset=false; Bluetooth=false
I/HeadsetService( 1977): Selected configuration: speaker
I/HeadsetService( 1977): Headset=true; Bluetooth=false
I/HeadsetService( 1977): Selected configuration: headset
V/WiredAccessoryManager( 1746): Headset UEVENT: {SUBSYSTEM=switch, SWITCH_STATE=0, DEVPATH=/devices/virtual/switch/h2w, SEQNUM=12164, ACTION=change, SWITCH_NAME=Headset, SWITCH_TIME=9817830244064}
V/WiredAccessoryManager( 1746): newName=Headset newState=0 headsetState=0 prev headsetState=1

This makes the handset almost impossible to use for calls without workarounds.
I understand that this is a common problem and that it has been addressed by more than one application in the Market store.  Still, those applications I have tried have not worked correctly to eliminate this problem.
I can't physically clean the port at the moment, and I would like do do this 'manually' via the shell.
Isn't there a straightforward way to do this?  I have tried with the activity manager and package manager search and try to get and set relevant data, but I haven't seen a way to say something like:
    localhost / # am kill HeadsetService
    localhost / #

-which does not stop the flip-flopping device detection.
Can I just echo something to a file like '/sys/devices/virtual/switch/h2w/state' and then use chattr to make it immutable?  Is that even the right file for the wired audio headset?
EDIT:  This doesn't work:
    localhost / # chattr +i !$
    chattr +i /sys/devices/virtual/switch/h2w/state
    chattr: reading flags on /sys/devices/virtual/switch/h2w/state: Not a typewriter
    localhost / #

Why not just clean the port?

I'd like to know how one does so (disables such a device) at the OS level.
Anyway, I have tried to do so without taking the thing apart.  I don't currently have access to a tool with which to take it apart.

That's very probably not possible*. The root cause is identified so I'd suggest you just fix the root of the problem (dirt) and not apply band aids in the wrong place (trying to disable it at the OS level). (* It may of course be possible using mad haxor skillz, but i don't think it'll be worth researching and applying them to this type of problem)


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where can i get app back that opens a tab for all my apps?
My smartphone was open in my pocket and the application that opens the tab for my all apps disappeared. Now i can open apps that are not on the home screen just through the play store.
phone sony xperia xz2 compact, android pie 9

Usually, there's always a way to open the app menu from the home screen (e.g. by dragging from the bottom of the screen). However, without much information, it's almost impossible to guess the cause. At the very least, could you provide the phone model, the Android version, and whether you're using 3rd-party launcher or not? Additionally, a screenshot of the problem might help.

Not my phone but I drew a red circle around what's missing.  Can I get that somewhere back? Without it i can't find any others means to launch my apps tha play store. (phone sony xperia xz2 compact, android pie 9)

thanks very much Andrew T. looks like i can open that tab by dragging from the bottom of the screen.


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Running dex2oat on host computer
I have compiled dex2oat on linux-x86_64 for linux-x86. I can run it just like a normal application. The background is, I have a tool which can generate dex codes and I want to perform some basic checks that dex2oat does. So it is not important for me to get an actual runnable file.
I do get the following output:
dex2oat I  4183  4183 art/dex2oat/dex2oat.cc:1239] out/host/linux-x86/bin/dex2oat --runtime-arg -Xms64m --runtime-arg -Xmx64m --image-classes=frameworks/base/preloaded-classes --dex-file=/home/marc/Apps/Example1.apk --dex-location=bla.apk --oat-file=bla.oat --image=out.art --base=0x60000000 --instruction-set=x86 --instruction-set-features=default --runtime-arg -Xrelocate --host --android-root=out/host/linux-x86 --include-patch-information
dex2oat E  4183  4183 art/runtime/runtime.cc:1108] Failed to return pre-allocated NoClassDefFoundError
dex2oat F  4183  4183 art/runtime/thread.h:330] Check failed: new_exception != NULL
dex2oat F  4183  4183 art/runtime/runtime.cc:284] Runtime aborting...
dex2oat F  4183  4183 art/runtime/runtime.cc:284] Aborting thread:
dex2oat F  4183  4183 art/runtime/runtime.cc:284] "main" prio=5 tid=1 Runnable (still starting up)
dex2oat F  4183  4183 art/runtime/runtime.cc:284]   | group="" sCount=0 dsCount=0 obj=(nil) self=0xf89a8e78
dex2oat F  4183  4183 art/runtime/runtime.cc:284]   | sysTid=4183 nice=0 cgrp=user/1000.user/c2.session sched=0/0 handle=0xf6b76700
dex2oat F  4183  4183 art/runtime/runtime.cc:284]   | state=R schedstat=( 17496280 53788 15 ) utm=1 stm=0 core=7 HZ=100
dex2oat F  4183  4183 art/runtime/runtime.cc:284]   | stack=0xff0f1000-0xff0f3000 stackSize=7MB
dex2oat F  4183  4183 art/runtime/runtime.cc:284]   | held mutexes= "abort lock" "mutator lock"(shared held)

Does anyone know what causes this error or did I supply the wrong arguments?
I have added a cout statement in the code and it turns out that the class being searched for is Ljava/lang/Object;

It searches for a class, but can't find it. dex2oat seems to either be incompatible with your --image-classes or the dex file is invalid (the bla.apk one).

Taken from the android build process:
out/host/linux-x86/bin/dex2oatd --runtime-arg -Xms64m --runtime-arg -Xmx512m --boot-image=out/target/product/ranchu/dex_bootjars/system/framework/boot.art --dex-file=out/target/product/ranchu/obj/APPS/Telecom_intermediates/oat/arm64/package.odex.input --dex-location=/system/priv-app/Telecom/Telecom.apk --oat-file=out/target/product/ranchu/obj/APPS/Telecom_intermediates/oat/arm64/package.odex --android-root=out/target/product/ranchu/system --instruction-set=arm64 --instruction-set-variant=generic --instruction-set-features=default --include-patch-information --runtime-arg -Xnorelocate --no-generate-debug-info --abort-on-hard-verifier-error --no-inline-from=core-oj.jar


text:
Disable Client Isolation when using hotspot
I just moved to a new place and internet is not setup yet so I'm using my phone's hotspot to get online. While developing a Python client-server program I found out that devices connected to Android hotspot cannot communicate with each other. When I ping one computer from another I get a "Destination host unreachable" message. This must be some sort of client isolation. Does anybody know how to turn it off? Using latest crDroid on Android 9.
[UPDATE]
I run a few more ping tests and they seem pretty inconclusive. I got some hits but the results vary between 'Host unreachable', 'Request timed out' and various TTL times (6ms to 4000ms).

Android uses hostapd as its AP daemon. hostapd.conf file which AOSP creates doesn't contain ap_isolate=1. But may be your OEM has added that to configuration file. You can check that with root: cat /data/vendor/wifi/hostapd/hostapd_*.conf. Do you ping the hosts by IP or hostname?

@IrfanLatif I pinged the hosts by IP that I found from executing ipconfig on cmd. I found the hostpad_wlan1.conf file using a root browser and I can confirm that there is no ap_isolate=1 line in there. Maybe it's 1 by default and I should write ap_isolate=0? As I said I'm using a custom ROM so not sure what you mean by my OEM (wouldn't that be Xiaomi for example?).

Sorry I missed the custom ROM point. ap_isolate is not set by default. There must be some issues with your networking. Use tcpdump or iptables -j LOG for troubleshooting.

Updated the post with new data.

As I mentioned earlier watch traffic on both sides using tcpdump when pinging. Even better do ip n flush all and then use arping and watch. See the state of arp requests on both sides. That would give some clue where the problem is.

I have tried with Android 9 by HTC and the connection between clients works. Although I had to wait for it for about 2 minutes (been waiting on a ping loop).

I can confirm that with enough patience, it starts to work (HTC U11), which is quite confusing. I always assumed AP isolation is enabled until reading @OndraŽižka's comment.


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Log off animation in Pac-man rom
How can i change the default log-off animation in my nexus4(PAC man ROM). I was able to change the boot animation in data folder but unable to find the logoff animation.

Try this: How to Change Shutdown animation
As it says, you'll find the location of the animation is "/system/media/video/shutdown"

But i cannot find /system folder in my root

Is there not a video/shutdown folder structure just where your boot animation exists? Both of these are supposed to be at the same location. If not, I'm not sure where else to find the same, as I have not used the PACMan ROM.

I'm not sure about your device specifically, but the structure i have is a bootanimation.zip & SHUTanimation.zip


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4.3 OTA Update Install Fail With Motochopper Root 4.2.2 Google Nexus 7
I am using Stock Android 4.2.2 on Nexus 7 2012 Tablet. I rooted my tablet using the Motochopper Root. I was able to download OTA 4.3 Update using normal procedure on my tablet however, when I tried installing the update, it just stuck at the android guy with error at startup. I tried downloading the OTA update again as it just disappeared, however it is stuck at waiting to download. I tried Nexus Tool Kit downloaded Stock 4.3 OTA and tried to install it using ADB sideload command. However it gave an error and mentioned some error file and exited. Please Help me out . I also tried full unroot with SuperSu but it also did not work.

Download stock ROM from Google, and flash it.
To check correct version for your Nexus 7 2012, see this question.
Since it would now be stock, you'd have to root it again.

I dont want to lose any data.

How do I achieve that??

@aibk01 If you can still connect your tablet to a PC and access the files in it, copy them. Otherwise, too late. It is recommended to always backup before doing something that might break your phone, like rooting or flashing a different ROM. I'm afraid you'll have to do a factory reset (in recovery mode) before flashing a new ROM.


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Port already Using Error in Android
I have an android application which is running on Huawei S7,Android 2.2. It is getting inputs from an arduino board.Arduino Board is connected to the tablet by USB cable.Application is using USB Protocol to connect to arduino.
The application is written for Android 4.1.And it is using a backward compatibility pack to make it runnable on 2.2. We had to use a 2.2 device.But now we have a device with Android 4.3. And when we try to run the same app in 4.3 device it gives an error saying 4567 port already in use. 4567 port is the port used by arduino application to connect with the Android Device(Tablet Application).
How can i find the application which is using the 4567 port?
Is there any way i can free up that port?
My 4.3 device is not rooted. Will rooting do any good in this problem?

You could check whether the netstat binary is available on your device. It's a command line tool, so you'd either need a terminal app or an ADB connection to use it. netstat --tcp --listening -p then should list up all listening ports together with the associated "program" (didn't try this on Android, so I'm not sure whether all options are supported. If you can confirm this, I'll write up an answer).

I used terminal emulator app and ran the above command.
This is the output i got.
https://drive.google.com/file/d/0B8JZMxx6Km7oZFpqRGJkcUV0cDQ/edit?usp=sharing

Do i need the root access to run this command?

Just a second: Your linked screenshot does not use above command. You ran lsof (LiSt Open Files). I wrote netstat --tcp --listening -p. Complete different commands, for different purposes (though partly overlapping). Please ty again :) And no, it should not require root to run netstat (though the -p parameter might ask for it, depending on implementation).

Sorry i linked the wrong screen shot. I was trying that command suggested by another stackexchange site user.This is the one i got when running netstat --tcp --listening -p
https://drive.google.com/file/d/0B8JZMxx6Km7od1BzN1BaR1ZGNWc/edit?usp=sharing

OK, that makes more sense. If I interprete it correctly, there's either nothing listening on any TCP port altogether – or at least nothing you have access to. As indicated by my last comment, -p might require root permissions (at least according to its man pages). Try again without that parameter to see whether the list is really empty. If not, you've found out if rooting will do any good in this problem ;)

These are the outputs i get when i try that without the -p
#1 - https://drive.google.com/file/d/0B8JZMxx6Km7oalJtaUVvVkdQd1E/edit?usp=sharing
#2 - https://drive.google.com/file/d/0B8JZMxx6Km7oMy04TnB3QXlIeG8/edit?usp=sharing
#3 - https://drive.google.com/file/d/0B8JZMxx6Km7objRONnR3MEUwM1E/edit?usp=sharing

In that case, my assumption was correct and -p requires root. -p would show you the app along the result list's entries, so you could figure out which app stands behind it. Looks like without root that's not possible – at least not in this way. But I've just found an app that might do the trick: NetStat Plus. You might wish to give that a try.

Without any additional tools, this should be possible via adb shell or a terminal app, using the netstat command: netstat --tcp --listening -p should list up all listening ports along with the app behind it. But it might very well be (as in your case, obviously) that the -p parameter requires root; and without it, the output won't show the app holding the port open.
However, NetStat Plus might offer what you need:

NetStat Plus and Connection List (source: Google Play; click for larger image)
I did not try this app myself, but the screenshots suggest it does exactly what you need: Listing apps with the used ports and status along. No word that it requires root. It further seems to work at least from Gingerbread (2.3.6 is explicitly mentioned) onwards to at least Jelly Bean 4.3 (also explicitly mentioned). An alternative would be Connection List (second screenshot).

I tried both the apps but any record they generate doesn't show any app using the port 4657. :(
Shall i give the screen shots of those too?

I don't think that will help. At least the screenshot of Connection list shows it deals with ports in LISTENING mode as well. So if no such is shown with any of the apps (and netstat --tcp --listening | grep ":4657" doesn't yield a result either, then there isn't anything listening there. Maybe some outgoing session was just using the very same port? Have you checked that? If that's the case, it might already be freed again. Try to start your app again. If it fails with the same error, use one of those apps to check for all entries with that port (not only LISTENING).

I ran the netstat --tcp --listening | grep ":4657" command and got this result.
It has 4567 in it but the complete port number is 45675.I guess it's not the same.
https://drive.google.com/file/d/0B8JZMxx6Km7oMU5NREhldEQwZjA/edit?usp=sharing
https://drive.google.com/file/d/0B8JZMxx6Km7od3RuMjlJLU1CNk0/edit?usp=sharing

It is as much the same as 4,657 USD and 46,575 USD are the same :) Please, try again with your app. If it shows the same error, check with the apps again as described (and optionally netstat --tcp | grep ":4657" for the general information whether the port is in use, and if so, in which state). Assuming either ESTABLISHED or CLOSE_WAIT, another app could be using it for outgoing connections.


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Data Recovery - Is the internal sd-card part of /data (gs4)?
On every other phone I have owned (with CWM recovery) when I did a factory reset, it left my (internal) SD card contents intact.  I wasn't thinking and did a factory reset and deleted everything.
As you all know reformatting a hard drive doesn't actually wipe the drive.  From the looks of things the internal sd card is part of /data.  So I took data's block device and did the following from ADB shell
I'm not looking up the exact paths but I believe I determined the block device to use by looking at "busybox df -h"s output
dd if=/dev/*--PATH-TO-mmblk-WHICH-DATA-IS-ON/ of=/cache/img1.img bs=1M count=1024
tar cvzf /cache/img1.tar.gz /cache/img1.img
*Copy img*.tar.gz to network share on my comp with ES file explorer
rm -f /cache/img*

dd if=/dev/*--PATH-TO-mmblk-WHICH-DATA-IS-ON/ of=/cache/img2.img bs=1M count=1024 offset=1024
tar cvzf /cache/img2.tar.gz /cache/img1.img
*Copy img*.tar.gz to network share on my comp with ES file explorer
rm -f /cache/img*

dd if=/dev/*--PATH-TO-mmblk-WHICH-DATA-IS-ON/ of=/cache/img3.img bs=1M count=1024 offset=2048
tar cvzf /cache/img3.tar.gz /cache/img1.img
*Copy img*.tar.gz to network share on my comp with ES file explorer
rm -f /cache/img*
,
.
.

I did this with all 10 or so GB of /data/ (forget actual size, but it's a 16GB model).  I then opened these up in a hex editor and searched for known strings in my saved data (contents of messages from SMS backup & restore).  I was unable to find my data.  As far as texts are concerned I was able to find raw texts on my current device (not before I reset),
My question is, is the internal sd card on a different partiton than /data/?

It appears that the internal SD card is on the same partition as /data (I verified with my GT-I9500 at XXUEMJ9 - 4.3, output below):
root@ja3g:/storage/emulated/legacy # df
Filesystem               Size     Used     Free   Blksize
/dev                   931.8M    76.0K   931.8M   4096
/mnt/secure            931.8M     0.0K   931.8M   4096
/mnt/asec              931.8M     0.0K   931.8M   4096
/mnt/obb               931.8M     0.0K   931.8M   4096
/system                  2.7G     2.1G   588.6M   4096
/efs                    19.7M     9.2M    10.5M   4096
/cache                   2.0G    32.6M     1.9G   4096
/data                    8.8G     8.3G   540.4M   4096
/persdata/absolute      11.8M     4.2M     7.6M   4096
/mnt/shell/emulated      8.8G     8.3G   520.4M   4096
/mnt/shell/container     8.8G     8.3G   520.4M   4096
/mnt/ntfs              931.8M     0.0K   931.8M   4096
/storage/emulated      931.8M     0.0K   931.8M   4096
/storage/extSdCard      14.8G    10.4G     4.4G   8192
/storage/emulated/0      8.8G     8.3G   520.4M   4096
/storage/emulated/0/Android/obb     8.8G     8.3G   520.4M   4096
/storage/emulated/legacy     8.8G     8.3G   520.4M   4096
/storage/emulated/legacy/Android/obb     8.8G     8.3G   520.4M   4096

Some other manufacturers have different implementations of the layout; in fact, this decision was the largest possible reason why the Mass Storage option disappeared and MTP had to be used - because /data used ext4 which most Windows PCs can't recognize.
Some CWM versions do not perform a format on /data when you request for a factory reset - that is because they are either:

Running on a pre-3.0 version of Android that uses the older implementation
Using a manufacturer-defined custom layout
Running custom "Factory Reset" code that does only rm -rf on the folders

As to why the plaintext cannot be found, I'm not entirely sure - but I thought it might have to do with the formatting being done with secure erase (MMC_CAP_ERASE).
More information can be found here: http://teamw.in/DataMedia
And in the 4.2 source code itself: https://android.googlesource.com/platform/docs/source.android.com/+/android-4.2.1_r1/src/tech/storage/index.md


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Unpacking and repacking boot.img changes it's file size
So I unpacked boot.img file using unpackbootimg in ubuntu. Then without changing the file I repacked it. But the filesize became smaller. From 36.7 MB to 17 MB. I tried to flash that image to my phone. But it failed. Also ramdisk file was empty after unpacking the boot.img.
Note: This specific rom is a rom from Symphony i97. It has Spreadtrum UNISOC SC9863 chipset. And I unpacked this rom using spd research tool. Also this phone's fastboot and adb commands are tempered so most of the commands don't work. Most of the time it says unknown command or not implemented.

Ubuntu's package is outdated. Use AIK or magiskboot.

Actually I already used AIK. While using AIK I got an error message saying "The system cannot find the batch label specified". So it seems that this boot.img isn't a normal one. So is there any way to manually decompress the file and extract file data?

That error indicates a problem with your .bat file, not the boot.img. The batch file you downloaded with AIK couldn't run. Check that file (unpackimg.bat) for errors or you may also use AIK on Linux and Android.

okay. So after reading magisk notes. I think I know why there was no ramdisk. But the problem is even though I patched my recovery image using magisk it won't flash. And yes file size still became small. From 40 MB to 25 MB

Please explain it won't flash. Size may get smaller, contents should be complete. Which device you are on? Is it A/B, system-as-root, treble? Android version? What's the purpose of unpacking boot.img?

It's symphony i97. It's a new phone with new Speadtrum Unisoc SC9863 chipset, Android version 9.0, reason for unpacking is for rooting the phone and adding a custom recovery. Tried flashing using spd research tool. Because fastboot won't listen to the commands given.

No experience with SPD, so can't say anything for sure. Better add that device related info to question.


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Long term beacon ranging causes Bluetooth failure
We have an Android app that does beacon scanning using altbeacon  This can be with the app in the foreground or background.  After some random time interval (usually hours, but not always) of beacon ranging the Bluetooth will stop working.  At that point no Bluetooth devices, beacons or otherwise, can be detected.  It requires Bluetooth to be turned off and back on before BT works and beacons are detected again.
Other beacon scanner apps from the store also fail to detect any beacons when this issue occurs.
We added BluetoothMedic from altbeacon, but it never detects a problem.  The issue seems to occur on Moto g6 (OS 8) and Moto g7 (OS 9) phones.  Have not seen the issue on a Google Pixel 3 (OS 10) or Samsung S8 (OS 8).
So, the question is, is there a way to detect Bluetooth being on, but failing to detect devices?  If we can do that, we can trigger a Bluetooth power cycle to correct the issue.  Better yet, is there something that can be done to prevent the problem in the first place?  Looking online this type of failure seems to be not uncommon with the solution being a Bluetooth power cycle.
Thanks for any help.

Do you have any log that may indicate what is going wrong? For example the Bluetooth daemon may crash.

None of our logs are showing any crashes, unfortunately.  Then we'd at least know something went wrong.  Thanks.


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Battery icon has a question mark in it
I checked a lot of forums, like a lot, but no one had my exact problem. I have an ASUS Tablet with Android 4.2.2 and the battery icon in the notification bar has a question mark in it. At least when it turns on cause ocasionally it crashes on boot and reboots itself before even reaching the lockscreen.
Anyways, when I'm lucky and it turns on, it eventually crashes and reboots after a few minutes. If it is on and I try to get to the battery settings, it crashes and reboots.
I didn't manage to get to the battery to check the contact, like most forums say, but I don't think it's the case as it's getting juice from it to turn on...
I tried reseting it by the way.

Does the tablet work while it is connected to a charger? As your tablet is older most likely the battery (and/or the battery controller) is defect -> hardware defect.

@Robert No..not really. When it's connected to a charger it just displays a battery with a question mark in it instead of the charging icon, but it does sometimes turn on without a charger. Very strange...

Ok, then your battery is definitely dead. You have to replace the battery (e.g. in a repair shop) or buy a new tablet.

@Robert I understand...but why does it turn on when it's not connected to a charger?

Looks like the OS fails to get the battery info from its sensor, thus returning a question mark. Perhaps the battery is not totally dead yet, but it's already broken until the OS can't even recognize its value.

There can be three reasons for this:

Your battery is dead or the Battery Status Indicator (BSI) pin on your battery is faulty. In either case, you have to replace the battery.
The BSI pin head on your phone hardware is faulty.
The firmware on your phone has a bug, and is unable to properly read the battery charge.

The third one is very less likely. The second option is less likely, but in my case (a Samsung Galaxy On7), both 1 and 2 had occurred at the same time.


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How to hide the new gesture pill / navigation bar on my pixel 4a running android 11?
I m trying to hide the pill bar to get more screen real estate but I can't figure out how to do it.

The bar is highlighted in red.

Yes, I'm trying to hide everything related to the navigation bar on the bottom of my screen to have some sort of full screen experience. The gesture navigation is already active. It is showing a bar at the bottom which I don't want.

AFAIK, for Pixel/AOSP-based, there's no setting to hide the navigation bar completely. One of the ways to hide the navigation gesture bar is to enter the fullscreen/immersive mode. Some custom ROMs may provide this feature built-in (Lineage OS provides this on Nexus 5). Otherwise, 3rd-party apps may help (ref: Force an app to full-screen mode)

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.


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When I connect my phone to my laptop using USB connection, I can't get either of them to recognize the other?
I've tried turning on usb debugging and updating usb drivers from device manager and nothing happened. I've also tried connecting the phone to an Acer Chromebook 15 that I own and still can't get the phone or the laptop to recognize other. Only the charging worked in both cases.
There isn't any notification in the notification areas.
The phone in question is the Pixel 4a with Android 13 and the laptop is the Lenovo Ideapad 3 15ALC6 with Windows 11.

You might want to try different USB cables: Google Pixel 4 doesn't work with some USB cables (Update: Google responds)

I've tried connecting it with the cable that comes in the box and the only thing that happens is that the phone starts to charge.

For Windows, you possibly need to install Google USB driver. However, Chrome OS shouldn't require additional configuration, so the cable might really be the culprit, even if it's the one from the box.

I've tried with a Samsung Galaxy A12 from a friend and the Samsung recognized it as soon as I plugged it in and show me popup about data and file transfer access on both the Acer and the Lenovo.


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Hiding WhatsApp display picture of a certain user
I have Android 9 in my phone and have WhatsApp version 2.19.258 installed on it.
Now, I wish to hide/change the display picture of a certain contact, say Mr. Alex on my phone. How do I go about doing it?
Thanks!

You can't change someone else's profile picture on WhatsApp. You can only change your own. There was a bug in WhatsApp that used to show whatever photo you add to the contact in your phone's contacts app instead of their actual profile picture on WhatsApp but now it's fixed I guess.


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Activate location for "Find my Device"
When I go to https://www.google.com/android/find?u=0 (Find my Device), it says "Online" and "Location Turned Off" (under the device name) and the device is not located on the map.
I have checked the following on the device:

Settings->Security & Location->Find My Device: is "On"
Settings->Security & Location->Location->Use Location: is "On"
Wifi and mobile data are on (I have Internet connection)
The device knows its location (in Google Maps)
Find My Device can make my phone ring remotely.

Note: Sometimes the map shows the device (and the message becomes "Last seen ...") but this happens only rarely and under unpredictable circumstances (and a reload of the webpage makes it go back to "Location Turned Off" even if the phone was not moved and no settings were changed).
My device is an Umidigi A5 Pro with Android 9.

are you using same account?

@rajkavadia Yes. Find My Device successfully sees the phone ("Online") and I can make it ring. I just cannot get the location.

In addition to enabling location services, the "battery saver" mode must be off.
In battery saver mode, location services will be automatically deactivated when the screen is off (Android Help). Unfortunately, Find My Device is not clever enough to deactivate batter saver mode for determining the location.
I did not find a way to use Find My Device while at the same time being able to extend battery life.

I am not going to argue about your answer, it is correct, but "Battery Saver" isn't really intended to extend battery life, it is to keep the device minimally usable if the battery level falls below a certain level or is likely (base on previous usage) to run out before the next typical charge and should not be active all the time under normal use. Things like Adaptive Battery are intended to help minimize battery usage during day to day use to extend battery life. If your device isn't meeting your battery life needs, maybe look into why it isn't with a tool like GSAM Battery Monitor?

@acejavelin That doesn't really make sense to me... If the battery saver reduces battery consumption on an almost empty battery, then it stands to reason that it also reduces battery consumption when the batter is still full. Of course, there is a tradeoff (reduction of background features such as synching) but I'm happy with that if it gives a day or two extra battery life.
And even if one does not want the battery saver on the whole time, I think the inability to locate the phone is still a serious problem because one might lose the phone while having low battery.


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DivestOS Mobile recovery image gives error on Heimdall
My Samsung Note 3 SM-N9005, the first time I used Heimdall I could successfully flash the recovery image from here (particularly this image). Now in download mode is current binary: custom and system status: custom, but when I go into recovery mode I get the standard one without install.
So I thought that the recovery partition got overwritten by the subsequent boots and I tried to flash it again to then immediately boot from recovery, but Heimdall keeps giving me ERROR: libusb error -7 whilst receiving bulk transfer, even if I can download PIT with no problems.
I've tried this on Windows 10, 8.1 and 7 with the same result.
Also, I have tried Odin on Windows 8.1 and Windows 7, in both device get added in Odin in Download Mode, but it crashes when trying to flash recovery img.

Sorry? I'm new to this forum and maybe missed some guidlines. Help on the topic appreciated, thanks

Which version of Hemidall are you using? I had a similar issue with 1.4.0 (from deb packages), fixed using 1.4.2 (here might appear other solutions)

Yes I was using 1.4.2 too


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Golden Dict problem with Android 12?
I have Golden Dict lite ver 1.6.6 installed on a Denver tablet (Android 8) working fine, but when I tried on a new tablet (Lenovo M9), it just stopped whenever I tried to use it, since this dictionary is not under development any longer, there's no way for me to get a newer verion.
problem: Golden dict and Moon Reader are installed on my device, whenever I tried to use Goldendict within Moon Reader, it pop-up then a message came up saying that the dictionary stopped working, then quit the app.

Hi, please note that questions directly asking for app recommendations are off-topic. Instead, we prefer the asker to just state the underlying problem that they want to solve and not put any restriction for apps-only, so we'd appreciate it if you could [edit] the question, add some details, and/or remove the restriction. Otherwise, you might be interested in our sister site, Software Recommendations Stack Exchange instead. Thanks.

Thanks for your comment.

If an app doesn't work on a newer Android version and the app is no longer maintained there is only one thing yo can do: uninstall it. The app was developed for about Android 6 and between 6 and 12 a lot of fundamental changes have been introduced to Android that require changes on code level within an app.


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Replace default preinstalled Google apps safely
I have a Redmi 9C with Android 10, it came with several pre-installed apps from Google and Redmi, I used ADB to un-installed some apps that I thought was safe, but for some reason, some of those apps came back without a system upgrade (that I'm aware of), and the developer options that I had set up previously was wiped out. I'm not that familiar with Android, so please bear with me, here are my questions:

can I replace safely "essential apps" (such as phone, SMS, downloader, etc.) with alternative ones? I was a Windows user until Windows 10, then switched to Linux after MS started doing OS upgrade on the background without user's permission, it seems Google is start doing the same, is there a site with updated/reliable info about this topic?
is there a tip/trick to "not allow" Google to re-install those apps that I removed? Why only some of the apps came back and not the others? Maybe because the apps I'm still using needs some libraries from the apps that I removed? For instance I can't remove Google Pay form ADB (it's not listed there), and I've removed Google Wallet, now Wallet is back again and not showing in ADB!

ps: 1) ADB - I'm using Xiaomi ADB/Fastboot Tools 7.0.3, it's a jar file with UI frontend, so I'm not using command line.
2) My bad, did not write down the package name, will do next time/next packages.

Please include the command(s) you have used for "uninstalling". Google Wallet is the new name of Google Pay.

The packageName of an app can be totally different from the app name displayed on the Andrroid UI (because the app packageName can later not be changed). To get a list of packageNames and how to get the app display name is shown here: https://stackoverflow.com/questions/16650765/get-application-name-label-via-adb-shell-or-terminal

thanks for the tips, I've updated my post.

As long as you have the Google Core apps (especially Google Services Framework) on the device, Google has the possibility to do such things. Depending on how far you wish to go, there are things like "unofficial installers" for microG which do the replacements (replacing the GSF by the open-source microG framework (I'm not sure which of those did take care of GSF removal, but vaguely remember there was one; microg-unofficial-installer only describes what it installs so it might not work with GSF present).

Thank you all for the feedback, I'll take a look at microG and tutorial on ADB commands (it seems the UI is outdated and not reporting properly the installed apps.)


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What is the FastBoot? and what is the difference to obtain the root on Nexus devices?
I have some doubts about fastboot and some other stuff.
I am an owner of an old HTC Desire on which, a long time ago, I installed Cyanogen Mod Android distribution.
Although I installed the Cyanogen I have many doubts about the fastboot and the Android architecture.
What exactly is FastBoot? What it is for?
I also have a doubt about how obtain root permission on the new Nexus 5, reading online I have understand that to obtain root permission on the Nexus devices I have to connect it to my PC and to execute a program that give me the root...but this is the same thing that I did on my HTC Desire.
What is the difference? Why many people say that obtain root permission on Nexus devices is easier than on others devices? It seems to me the same thing !!! What am I missing?

You've already used the correct tags. Their tag-wikis will answer most of your questions, e.g. the fastboot tag-wiki goes into details on what Fastboot is (for). Many of our tag-wikis contain such explanations or even first-aid hints, always worth a look ;) Not having a Nexus devices, I'll leave the remaining parts for others to answer.

Have a look at this answer: http://android.stackexchange.com/a/46682/30106. It should at least solve your queries for fast boot.

@naveen "fast boot" is not the same thing as "fastboot."

When talking about gaining root for a given device, it usually means obtaining it for the first time by developers. There are generally two ways of doing this. You can either find a software vulnerability that can be exploited to elevate permissions and sneak in the su (superuser) binary into write-protected system area, or you can flash an image of the device with root already in place. Needless to say, exploiting vulnerabilities is a lot more difficult. This is where fastboot comes in.
On some devices (mostly HTC and Motorola) Fastboot is a special start-up mode that allows you to flash pre-made images onto various internal memory partitions. It is similar to Samsung's "Download" mode, except instead of proprietary software like Kies or Odin (and Heimdall), it uses the fastboot utility that comes standard with Android SDK.
However, flashing can be, and usually is, restricted by device manufacturers to only images signed by the manufacturer themselves (or the carriers). This is what is referred to as bootloader locking. Most new phones ship with locked bootloaders, which makes it impossible to flash custom ROMs. You are back to having to root via the other, more difficult method.
Nexus devices come with unlockable bootloaders, so that you can flash ROMs easily and without restrictions.  Unlocking a bootloader of a Nexus device is very easy as well.  A pre-rooted image usually surfaces very quickly for these devices after they are released.
It is worth noting that with Android 4.3 (Jelly Bean) and even more so with 4.4 (KitKat) Google has changed some low level OS security policies, which renders old rooting methods obsolete. Unlocking the bootloader and flashing a modified image of the OS that circumvents these new policies will soon become the only way to really achieve root.  You can read more about this here.


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How to see the contents of boot partition
Does anybody know how to mount the boot partition?On my nexus 7, I booted to recovery and tried to mount the boot partition using the following-
mount -t ext4 /dev/block/platform/msm_sdcc.1/by-name/boot /boot
But this failed.
I tried to do read-only mount and mount using vfat, but with no success.


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How to activate car mode with a magnet?
The Google Nexus 7 tablet has lots of reed relays and magnets.
Some toggle the screen, others activate the wireless charging dock. I suppose there is a position for activating car mode (never putting screen to sleep). I'd like to put a magnet (or several if necessary) into my car dock, so I can trigger car mode, whenever I put the tablet in there.
Unfortunatelly, I couldn't find a page, that will describe the various positions of the reed relays inside the device.

the best way is NFC Trigger.. there is an app (nfc trigger) that can activate car mode automatically when the tag is close to the tablet

Yup, you can get NFC tags pretty cheap on the internet.


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Lookout - Which application is trying to access the system with no authorization
Is there any log where I can check which unknown source app is trying to access the phone without authorization? Lookout keeps popping up this message but don't tell me which application is! It happens whenever I connect to Wi-fi/3G. The application says that everything is normal after a scan. I don't want to remove all applications installed from unknown sources!
I couldn't get the message in english just switching the phone language, it only shows partially in english:

I don't use this Lookout app, so I cannot tell you whether it has this hint somewhere. But I can give you some clues how to "rule out innocent apps", so you don't have to "remove all applications". With some luck, this filtering leaves only a few candidates.
First indicator you gave: It happens whenever I connect to Wi-fi/3G. So it has to be a) an app with "some WiFi permission", which also listens to the "network changed" broadcast (to put it in easy words). So first let's check for apps with matching permissions:

Guardian Droid and Permission Explorer (source: Google Play)
Two helpful apps for this are Guardian Droid and Permission Explorer, as shown in the screenshots. They help you identify apps by permissions (and also apps with excessive permissions). Taking the Permission Explorer screenshot as a base here, your suspect app should be in one (or more) of the following groups: Internet, Access_Network_state. Most likely in both: it needs to know when Internet is accessible (so it's interested in the network state), and most likely wants to access it (Internet).
With this check, you will have ruled out some apps already. Probably not enough, as many/most apps will have the Internet permission even when not requiring it themselves – to load ads. So the next step is to check which of the filtered apps are listening to the "network state changed" broadcast (an indicator that your suspect does this is that the alert is triggered immediately when WiFi was connected, if I understood you correctly).

S2 APK Viewer and App Detective (source: Google Play)
For this we take a look at S2 APK Viewer and App Detective. Both of them allow to browse the Manifest of your .apks (Apps). Watch out for <receiver>s, which declare what broadcasts an app is interested in.
By these steps, you will not end up with the single candidate, but rather with several. But at least you don't have to check them all. As a broadcast listener can alternatively be declared dynamically by code (instead of in the manifest),  our friend might not be listed in the "reduced set" having applied all filters, but must be amongst those left over by the first (permission) scan.
Whilest not completely solving your issue, I hope this at least helped narrowing down candidates to an acceptable level.

As it turns out in this case, it still leaves ~200 candidates to check. So let me suggest something I should have thought of from the beginning: investigating Android's logs. There are multiple ways to do this, like using dedicated apps (CatLog, Gemini LogCat, and LogCat Extreme are good examples), or doing it via adb logcat (requires ADB to be setup on your computer, see Is there a minimal installation of ADB?). If something raises a security notification, it should show up in the logs at least as warning (so you can restrict your investigation to this loglevel and higher ones). Most of the LogCat apps let you setup filters via their GUI. For the command line tool, you can take a look at its help page. Moreover, there's a nice article on "adb logcat" Command Arguments - Output Filters, which should be quite useful here.
Start the logcat viewer. If possible, clear "past entries" from the output, or set a mark (if the app offers this). After that, connect to WiFi. As soon as the warning pops up, stop log recording (or set the "end mark"). Now investigate the recorded lines. I'm positive this leaves much less than ~200 candidates – and wouldn't even be surprised you'd end up with an exact hit.

Thanks, but still I have 200 apps to analyze... Anyway, +1 for the tips.

That doesn't make it easy, admitted. Maybe adb logcat might offer some help then (no idea why I forgot about that). Let me update my answer accordingly.

I have a galaxy s4, I went to the settings,clicked more, then clicked security, then the section that says security update service I only checked the VIA Wi-fi Only box, clicked the home screen, turned off my wifi, turned it back on, clicked that security message that was on the notification bar, an update option came up, I clicked the update, agreed to the terms & conditions and now it never shows up for me anymore!! I also unchecked the VIA wi-fi only box after it updated just for my preference but i don't think its needed


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How can I transfer files between Samsung Galaxy Note 800 and usb pen drive?
Is it compulsory that I need a Desktop or Laptop to transfer files between Samsung Galaxy 800 and a usb pen drive.

No, there are other ways to copy files from a USB pen drive to a phone.
According to USB Host Diagnostics, the N8000 can support the USB OTG (on-the-go) cable, assuming you have the latest firmware. Just plug-in the USB pen drive (or USB stick) into it. This cable will cost you USD1 or less.
If you have root, you can use StickMount to make the mounting of the USB pen drive easier.


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How to select a power supply for a given Android device
There are a variety of products on the market which provide a power supply for Android devices through the ubiquitous MicroUSB 2 port.  These include adaptors for 12V "cigarette lighter" car DC power supplies, adaptors for AC (120-240V) domestic power supplies, solar power supplies, AA battery power supplies, and so on.
One consideration with all such products is the maximum current they can supply.  This is generally 500mA at a minimum, but I have seen up to 2 A.
How can we know what current our device will draw, so as to select a power supply which will maximize its recharge rate?  What is the maximum current that can be supplied via a MicroUSB connection?  How can we know if our device is able to safely use a power supply which can supply more current than it draws?

I'm not aware of any way to find out the maximum current the device will use except checking the charger that came with the device and assuming that the manufacturer suppied the most efficient charger suitable.
The maximum current for USB connection is 5A, but usually the range used by phone/tablet chargers is between 0.5A and 2A.
Note that the amperage of the charger only tells what is the maximum current that the charger can supply, so it's safe to plug a 2A charger to a device capable of 0.5A current.