Develop Reference

subprocess.check_output fails to execute a command but the same works in windows

I am trying to connect two devices to my pc and run some commands on them using python and adb.
when I run the command from the command prompt, it goes through fine, but when i put those in the python script, they give me errors.
this is causing the errors all the time:
from subprocess import check_output, CalledProcessError
try:
adb_ouput = check_output(["adb","devices","-l","|", "grep", "\"model\""])
print adb_ouput
except CalledProcessError as e:
print e
The error message I get is this:
Usage: adb devices [-l]
Command '['adb', 'devices', '-l', '|', 'grep', '"model"']' returned non-zero exit status 1
When I try the same code without the grep command, it works
adb_ouput = check_output(["adb","devices","-l"])
It gives me the right output.
When I try the same in windows command prompt, It works fine (I am replacing grep with FINDSTR because i'm using it in windows, and I have tried doing the same in the python script as well, with 'shell = True' and also without.)
eg:
adb devices -l | FINDSTR "model"
This gives me an ouptut without any problems.
The output I get is
123ab6ef device product:xxxxxxxxx model:xxxxxxxxx device:xxxxxxxxx
bd00051a4 device product:yyyyyyyyyy model:yyyyyyyyyy device:yyyyyyyyy
I am trying to understand where I am going wrong here, but can't figure it out.
So far I have checked the docs: https://docs.python.org/3/library/subprocess.html
https://docs.python.org/3/library/subprocess.html#subprocess.CalledProcessError
These just give me the error codes.
I have also looked at these answers:
Python, adb and shell execution query
I took some error checking from here and added to my code.
Python subprocess.check_output(args) fails, while args executed via Windows command line work OK
python check_output fails with exit status 1 but Popen works for same command
I think i am close but just can't put my finger on it.
Any help would be appreciated.

First
adb_ouput = check_output(["adb","devices","-l","|", "grep", "\"model\""])
certainly requires shell=True, but even with that it's not equivalent to
adb devices -l | FINDSTR "model"
When using check_output, you're passing "model" as grep argument literally but you should pass just model. "model" is not in your output (with quotes) so grep fails to find it, and returns exitcode 1 which is not really an error for grep but makes check_output trigger an exception because it expects 0.
So I would to this as a quickfix:
adb_ouput = check_output(["adb","devices","-l","|", "grep", "model"],shell=True)
And as a longfix I'd perform the grep command directly with python.
adb_output = check_output(["adb","devices","-l"])
for l in adb_output.splitlines():
if "model" in l:
print(l)

Obtain complete package name in android kernel mode

I am working on one project requires obtaining the complete app package name inside kernel mode. I realized the package name is also the process name inside kernel. However, the task_struct->comm (process name) can only give me 15 characters long.
Also, fs/proc/base.c proc_get_cmdline() can return the full process name but it is private function. I try to export proc_get_cmdline() to public and invoke from my loadable kernel module, but it always crash when I invoke the public proc_get_cmdline().
Is there any way I can get the complete package name inside kernel? Like read from proc/pid/cmdline, read from mm_struct, etc. Appreciate any code example.

You are not supposed to call proc_pid_cmdline().
It is a non-public function in fs/proc/base.c:
static int proc_pid_cmdline(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
However, what it does is simple:
get_cmdline(task, m->buf, PAGE_SIZE);
That is not likely to return the full path though and it will not be possible to determine the full path in every case. The arg[0] value may be overwritten, the file could be deleted or moved, etc. A process may exec() in a way which obscures the original command line, and all kinds of other maladies.
A scan of my opensuse 12.3 system /proc/*/cmdline turns up all kinds of less-than-useful results:
/proc/1/cmdline
/sbin/init showopts
/proc/10/cmdline
/proc/11/cmdline
/proc/1163/cmdline
/sbin/dhclient6 -6 -cf /var/lib/dhcp6/dhclient6.eth0.conf -lf /var/lib/dhcp6/dhclient6.eth0.lease -pf /var/run/dhclient6.eth0.pid -q eth0
/proc/12/cmdline
/proc/13/cmdline
/proc/14/cmdline
/proc/15/cmdline
/proc/16/cmdline
/proc/17/cmdline
/proc/1710/cmdline
/sbin/dhcpcd --netconfig -L -E -HHH -c /etc/sysconfig/network/scripts/dhcpcd-hook -t 0 -h del1-dhp-32429 eth0
/proc/172/cmdline
/proc/185/cmdline
/proc/186/cmdline
/proc/187/cmdline
/proc/19/cmdline
/proc/2/cmdline
/proc/20/cmdline
/proc/21/cmdline
/proc/22/cmdline
/proc/23/cmdline
/proc/25/cmdline
/proc/254/cmdline
/proc/255/cmdline
/proc/26/cmdline
/proc/2671/cmdline
/usr/lib/upower/upowerd
/proc/2674/cmdline
/usr/lib/polkit-1/polkitd --no-debug
/proc/27/cmdline
/proc/2727/cmdline
/usr/lib/udisks2/udisksd --no-debug
/proc/28/cmdline
/proc/285/cmdline
/usr/lib/systemd/systemd-journald
/proc/286/cmdline
/proc/288/cmdline
/proc/29/cmdline
/proc/2913/cmdline
/usr/sbin/cron -n
/proc/2924/cmdline
/usr/sbin/sshd -D
/proc/3/cmdline
/proc/3023/cmdline
/usr/lib/postfix/master
/proc/3090/cmdline
pickup -l -t fifo -u
/proc/3091/cmdline
qmgr -l -t fifo -u
/proc/31/cmdline
/proc/311/cmdline
/usr/lib/systemd/systemd-udevd
/proc/3132/cmdline
/usr/lib/vmware/bin/vmware-vmblock-fuse -o subtype=vmware-vmblock,default_permissions,allow_other /var/run/vmblock-fuse
/proc/3168/cmdline
/usr/sbin/vmware-authdlauncher
/proc/32/cmdline
Works for me in openSUSE 12.3:
for I in /proc/*/cmdline; do echo $I; cat $I | tr '\000' ' '; echo; done

Stopping android logcat that is executing in a child process

I am writing a ruby script in which I want to execute the android logcat -v time command in a child process and after some time kill the process (when the the parent is done doing xyz).
For example I have:
childpid = Process.fork {
adb -s <device-serial> logcat -c
adb -s <device-serial> logcat -v time>/path-to-file/forkLog.log
}
sleep(30)
#parent do thing else here ...
Process.kill("SIGHUP", childpid) #kill the child process
According to what I've read the adb logcat code is executed in another child sup-process, so when I try to do a Process.kill the childpid stops but its sub-process does not.
how do I kill the logcat -v time>forklog.log process from the parent process??

Typically, when you're using fork to call a bash script, you'll want to use Kernel::exec() instead of Kernel::system() or Kernel::`
Process.fork{exec('adb -s <device-serial> logcat -c && adb -s <device-serial> logcat -v time>/path-to-file/forkLog.log'}
The difference is that exec will replace the Ruby process with the shell script, while the other two will create a subprocess.

ADB Error codes

We have an android device and as part of testing I need to excute a console test application on the target device. If the test application detects an error it returns -1.
I can use adb shell to run the test applications remotely on the target but I can't find a way of getting back the return code. I need this so I that I can build this into an automated test suite.
I could try grepping the console output for some failure text but that is a bit grubby. Does anyone know of a more elegant solution?

This is a workaround to get the exit code:
adb shell '{your command here} > /dev/null 2>&1; echo $?'
This is a wrapper around adb in Ruby:
def adb(opt)
input = "#{adb_command} #{opt[:command]} #{opt[:params]}"
puts "Executing #{input}...\n"
output = nil
exit_code = 0
def wait_for(secs)
if secs
begin
Timeout::timeout(secs) { yield }
rescue
print 'execution expired'
end
else
yield
end
end
wait_for(opt[:timeout]) do
case opt[:command]
when :install, :push, :uninstall
output, exit_code = `#{input}`, $?.to_i
when :shell
input = "#{adb_command} shell \"#{opt[:params]}; echo \\$?\""
output = `#{input}`.split("\n")
exit_code = output.pop.to_i
output = output.join("\n")
else
raise 'Error: param command to adb not defined!'
end
end
return if opt[:ignore_fail] and output =~ /#{opt[:ignore_fail]}/
raise output unless exit_code == 0
end

You could use Facebook's fb-adb, a "A better shell for Android devices" which "propagates program exit status instead of always exiting with status 0".

Android/adb redirect console app output

I am trying to get the output of a WLAN driver control interface via adb shell on a motorola droid 2. The command is called wlan_cu. To run the command,I am using:
% wlan_cu -itiwlan0 -s /data/jay/stat.sh
Connection established with supplicant .../Connection> Bssid_list,
Connect, Disassociate, Status, Full_bssid_list, wPs/
Status : DISCONNECT MAC : f8.7b.7a.7b.b7.9b SSID : <empty>
BSSID : 00.00.00.00.00.00
Channel : <empty>
Driver/, Connection/, Management/, Show/, Privacy/, scAn/, roaminG/, qOs/, poWer/, eVents/, Bt coexsistance/, Report/, dEbug/, biT/, aboUt, Quit
[1] Segmentation fault wlan_cu -itiwlan0 -s /data/jay/stat.sh
The -s option is to read wlan_cu commands from a script.
% cat /data/jay/stat.sh
c s
/
q
If I try to redirect the output i.e.
% wlan_cu -itiwlan0 -s /data/jay/stat.sh &> out.txt
out.txt is created, but empty and the output still goes to screen. Anyone have an idea? been stuck on this for quite a while.

you can try to redirect both stdout and stderr to the out.txt. Try this,
# wlan_cu -itiwlan0 -s /data/jay/stat.sh > out.txt 2>&1