ssh/sshd hang after "debug2: channel 0: open confirm rwindow 0 rmax 32768"

[Bruce Allen]

Hi Damien,

Here's the tail of the sshd strace output that you asked for:

rt_sigaction(SIGHUP, NULL, {SIG_DFL}, 8) = 0
rt_sigaction(SIGHUP, {0x8062c49, [], 0}, NULL, 8) = 0
rt_sigaction(SIGTERM, NULL, {SIG_DFL}, 8) = 0
rt_sigaction(SIGTERM, {0x8062c49, [], 0}, NULL, 8) = 0
write(2, "debug3: mm_request_receive enter"..., 37debug3: 
mm_request_receive entering
) = 37
read(6, debug1: temporarily_use_uid: 501/500 (e=0/500)
debug1: restore_uid: 0/500
debug1: permanently_set_uid: 501/500
debug2: set_newkeys: mode 0
debug2: set_newkeys: mode 1
debug1: Entering interactive session for SSH2.
debug2: fd 6 setting O_NONBLOCK
debug2: fd 7 setting O_NONBLOCK
debug1: server_init_dispatch_20
debug1: server_input_channel_open: ctype session rchan 0 win 65536 max 
16384
debug1: input_session_request
debug1: channel 0: new [server-session]
debug1: session_new: init
debug1: session_new: session 0
debug1: session_open: channel 0
debug1: session_open: session 0: link with channel 0
debug1: server_input_channel_open: confirm session
0xbfe49080, 4)                  = ? ERESTARTSYS (To be restarted)
--- SIGCHLD (Child exited) @ 0 (0) ---
--- SIGCONT (Continued) @ 0 (0) ---
read(6,  <unfinished ...>


The sshd process is hanging on the read() from file descriptor 6.

Note 1: I did this by running 'strace sshd' on a nonstandard port (port 
2000) and then trying to make a connection to it.  As far as I can see, 
all the authentication is fine.  Just the connection itself fails.

Note 2: I didn't have any arguments to strace other than the sshd command 
line. Let me know if I need some options added, for example to follow 
forks or something.

Cheers,
 	Bruce


On Sun, 16 Mar 2008, Damien Miller wrote:

> On Sun, 16 Mar 2008, Bruce Allen wrote:
>
>> Hi Peter,
>>
>> A bit more information:
>>
>> (1) My hotel's IP (Pasadena Hilton, service from AT&T) is NOT properly
>> registered in DNS:
>>
>>     ballen$ nslookup
>>    > 12.191.122.167
>>     Server:         85.37.17.16
>>     Address:        85.37.17.16#53
>>     ** server can't find 167.122.191.12.in-addr.arpa: NXDOMAIN
>>
>> (2) On opensshd version 4.8, turning UseDNS off makes no difference.
>>      Is there some other config switch I should try?
>>
>> (3) I CAN connect to an opensshd version 3.6 ssh daemon.
>>
>> (4) As far as I can tell, the sshd_config files being used for the v 3.6
>>      and v 4.8 sshd servers have only unimportant differences.
>>
>> Any further thoughts or suggestions?  I have a few more days in the hotel
>> so I can try some other things.
>
> You could try to strace/truss or ltrace the server to see where it is
> stopping.
>
> -d
>