apt-get blocks on /dev/ptmx a lot

Thanks for your bugreport.

Do you have /dev/pts mounted when this happens? Could you please try to attach a gdb to apt-get and see if you get a useful backtrace where it sepends its time?

Thanks,
 Michael

backtrace:
#0 0xffffe410 in __kernel_vsyscall ()
#1 0xb7c9acb3 in read () from /lib/tls/i686/cmov/libc.so.6
#2 0xb7ede9d7 in pkgDPkgPM::DoTerminalPty ()
   from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#3 0xb7ee45ce in pkgDPkgPM::Go () from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#4 0xb7e90558 in pkgPackageManager::DoInstallPostFork ()
   from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#5 0xb7e905dd in pkgPackageManager::DoInstall ()
   from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#6 0x0805c2c8 in ?? ()
#7 0x0805f20b in ?? ()
#8 0xb7e73b2b in CommandLine::DispatchArg ()
   from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#9 0x0804ea1b in ?? ()
#10 0xb7bed050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#11 0x0804cec1 in ?? ()

% mount | grep pts
devpts on /dev/pts type devpts (rw,gid=5,mode=620)

Thanks for this additional information.

The man open /devptmx are a resource leak in the process that drives dpkg. I uploaded a fix for this today.

apt (0.7.6ubuntu14) gutsy; urgency=low

  * apt-pkg/deb/dpkgpm.cc:
    - fix resource leak (LP: #148806)

 -- Michael Vogt <email address hidden> Mon, 15 Oct 2007 20:57:44 +0200

Nice work! The one time I ran it today after the new apt package, it didn't lock up - but it wasn't something that happened every time, so let's leave it a day or two before saying it's fixed for sure.

Today I ran synaptic to remove a package, and dpkg went defunct :( I'm using the latest apt as of right now (0.7.6ubuntu14), and strace reveals that dpkg dies trying to read /dev/ptmx . some relevant info:

output from synaptic:
Removing kcontrol ...
Processing triggers for libc6 ...
ldconfig deferred processing now taking place

strace results:
root@ravana:~# readlink /proc/15359/fd/35
/dev/ptmx

Sorry, I managed to reproduce it by installing and then removing kcontrol again. and attach some useful info this time (hopefully!)

Also, devpts is mounted.
devpts on /dev/pts type devpts (rw,gid=5,mode=620)

Notable lines in the strace file:
3180ish to the end = Input/Output errors just before the read() hang

The last few lines for the impatient :)

select(28, [0 25 27], NULL, NULL, {1, 0}) = 1 (in [27], left {1, 0})
read(27, 0xbfd29078, 1024) = -1 EIO (Input/output error)
waitpid(16621, 0xbfd316c4, WNOHANG) = 0
---snip lots of these---
select(28, [0 25 27], NULL, NULL, {1, 0}) = 1 (in [27], left {1, 0})
read(27, 0xbfd29078, 1024) = ? ERESTARTSYS (To be restarted)
--- SIGCHLD (Child exited) @ 0 (0) ---
read(27,

here's a backtrace of apt-get on another `apt-get install kcontrol` (had to kill the one I got the strace from(
(gdb) bt
#0 0xffffe410 in __kernel_vsyscall ()
#1 0xb7d50cb3 in read () from /lib/tls/i686/cmov/libc.so.6
#2 0xb7f949d7 in pkgDPkgPM::DoTerminalPty () from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#3 0xb7f9a5ce in pkgDPkgPM::Go () from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#4 0xb7f46558 in pkgPackageManager::DoInstallPostFork () from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#5 0xb7f465dd in pkgPackageManager::DoInstall () from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#6 0x0805c2c8 in ?? ()
#7 0x08060eb2 in ?? ()
#8 0xb7f29b2b in CommandLine::DispatchArg () from /usr/lib/libapt-pkg-libc6.6-6.so.4.5
#9 0x0804ea1b in ?? ()
#10 0xb7ca3050 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#11 0x0804cec1 in ?? ()
(gdb)

HTH, and feel free to let me know if there's any other info that would come in handy :)

@Troy C: thanks for this information, that looks very good. What did you do to reproduce the problem? I'm not able to reproduce it here currently.

Simply doing `apt-get install kcontrol` and then `apt-get remove kcontrol` will cause the problem, anywhere between 10%-40% of the time.

for i in `seq 1 50` ; do apt-get -y -qq install kcontrol ; echo "install $i OK"; apt-get -y -qq remove kcontrol; echo "remove $i OK"; done

As others have mentioned, there's no immediately obvious pattern to which iteration will hang.