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#43 ssh -t hanging

open
nobody
None
5
2011-10-06
2011-10-06
henry barber
No

I'm having some strange behaviour from OpenSSH
It presents itself when using the "ssh -t" / pseudo terminal.
We are using this feature to update the wtmp and it is working fine on SuSE and RH, but our AIX hosts are getting hung. The first attempt is usually successful, but eventually, the session is hung and the CRTL-Z does not put the process into background.
The ssh -v output

OpenSSH_5.4p1, OpenSSL 0.9.8m 25 Feb 2010

and when I run a truss:
[snipped]
kwrite(4, " �9E � d � � e 9 � O\b �".., 576) = 576
_select(5, 0x2005DC28, 0x00000000, 0x00000000, 0x00000000) = 1
kread(4, " �8E07 y � � � } � < � �".., 8192) = 32
kfcntl(0, F_DUPFD, 0x00000000) = 5
kfcntl(1, F_DUPFD, 0x00000000) = 6
kfcntl(2, F_DUPFD, 0x00000000) = 7
kioctl(5, 22528, 0x00000000, 0x00000000) = 0
kioctl(6, 22528, 0x00000000, 0x00000000) = 0
kioctl(7, 22528, 0x00000000, 0x00000000) = 0
kfcntl(5, F_SETFD, 0x00000001) = 0
kfcntl(6, F_SETFD, 0x00000001) = 0
kfcntl(7, F_SETFD, 0x00000001) = 0
kioctl(6, 22528, 0x00000000, 0x00000000) = 0
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(1, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000013, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(1, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000014, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(1, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(1, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000018, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(2, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000013, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(2, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(2, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(2, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(3, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000014, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(3, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x0000001B, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(3, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000013, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(3, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(15, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000015, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(15, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000015, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(15, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x00000019, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(15, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x0000001A, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(28, 0x00000000, 0x2FF21B60) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x0000001E, 0x00000000, 0x00000000) = 0x00000000
sigprocmask(2, 0xF0277960, 0x2FF21AB0) = 0
_sigaction(28, 0x2FF21B50, 0x00000000) = 0
thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9, 0x00000000, 0x0000001B, 0x00000000, 0x00000000) = 0x00000000
kioctl(0, 22528, 0x00000000, 0x00000000) = 0
kioctl(0, 21505, 0x2FF21B50, 0x00000000) = 0
kioctl(0, 22528, 0x00000000, 0x00000000) = 0
kioctl(0, 21507, 0x2FF21B50, 0x00000000) = 0
_select(8, 0x2005DC28, 0x2005EBB8, 0x00000000, 0x00000000) = 1
kwrite(4, " � � >9A06 � 0 L 319 �92".., 128) = 128
_select(8, 0x2005DC28, 0x2005EBB8, 0x00000000, 0x00000000) = 1
kread(4, " � � c � g :1D1B �11 � 9".., 8192) = 48
kioctl(0, 1074295912, 0x2FF21A04, 0x00000000) = 0
getsockopt(4, 6, 1, 0x2FF219D0, 0x2FF219D4) = 0
setsockopt(4, 6, 1, 0x2FF219D0, 4) = 0
ngetsockname(4, 0x2FF21480, 0x2FF21988) = 0
setsockopt(4, 0, 3, 0x2FF219D0, 4) = 0
_select(8, 0x2005DC28, 0x2005EBB8, 0x00000000, 0x00000000) = 1
kwrite(4, "96 C C F v � Q l � �\f".., 384) = 384
_select(8, 0x2005DC28, 0x2005EBB8, 0x00000000, 0x00000000) (sleeping...)

Discussion

  • henry barber
    henry barber
    2011-10-06

    just to clarify - the ssh -t works fine with interactive commands - I've tried vi and smit - just fine; it's when running a non-interactive command that we get an (eventual) hang