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Praseed V Gopal

2008-May-30 19:11 UTC

"ERR sshd: error: no more sessions" issue

Initially send this mail to user group. then realized this is more apt
place. Apologies for posting in both groups...

Hi all,
We're using openssh version 4.7p on our linux 2.6-22 kernel.
We have a Java based GUI that opens a secure shell connection to this linux box.
To do something over the connection, the GUI opens a session (some
times 3-4 simultaneous sessions) & once done, it will close the
connection gracefully (I believe).
The problem is after a few sessions (10) are open & closed, we see
"May 29 14:43:11 ERR sshd[534]: error: no more sessions" error.
So I checked the source code of openssh & changed the value of
MAX_SESSIONS  from 10 to 100.in session.c @ line number 132.

Things got improved, but now after number of sessions crosses 100, the
same error pops up.
I enabled the debug mode. Debug messages are at the end of this mail.

1) Please tell me, whether the sessions are getting closed properly?
 2) If yes, why it is not decrementing the used sessions & reusing the
already closed sessions?
3) is this supposed to work this way?
4) How do I fix it or work around this?

Thanks & Regards
Praseed.

============Debug Messages===============May 29 14:43:07 DEBUG sshd[534]:
debug1: session_open: session 98:
link with channel 98
May 29 14:43:07 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:07 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 98 request exec reply 1
May 29 14:43:07 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:07 DEBUG sshd[534]: debug1: session_input_channel_req:
session 98 req exec
May 29 14:43:07 DEBUG sshd[534]: debug2: fd 105 setting O_NONBLOCK
May 29 14:43:07 DEBUG sshd[2514]: debug1: permanently_set_uid: 0/0
May 29 14:43:07 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len 0
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: read failed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: close_read
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: input open -> drain
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
delayed efd 107/(0)
May 29 14:43:07 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:07 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:07 DEBUG sshd[534]: debug1: session_by_pid: pid 2514
May 29 14:43:07 DEBUG sshd[534]: debug1: session_exit_message: session
98 channel 98 pid 2514
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: request
exit-status confirm 0
May 29 14:43:07 DEBUG sshd[534]: debug1: session_exit_message: release
channel 98
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: write failed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: close_write
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: output open -> closed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: ibuf empty
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: send eof
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: input drain -> closed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: send close
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: rcvd close
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: gc: notify user
May 29 14:43:07 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:07 DEBUG sshd[534]: debug1: session_close_by_channel:
channel 98 child 0
May 29 14:43:07 DEBUG sshd[534]: debug1: session_close: session 98 pid 0
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: gc: user detached
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: garbage collecting
May 29 14:43:07 DEBUG sshd[534]: debug1: channel 98: free:
server-session, nchannels 99
May 29 14:43:07 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1409 win 30000 max 33976
May 29 14:43:07 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:07 DEBUG sshd[534]: debug1: channel 98: new [server-session]
May 29 14:43:07 DEBUG sshd[534]: debug1: session_new: session 98
May 29 14:43:07 DEBUG sshd[534]: debug1: session_open: channel 98



May 29 14:43:07 DEBUG sshd[534]: debug1: session_open: session 98:
link with channel 98
May 29 14:43:07 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:07 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 98 request exec reply 1
May 29 14:43:07 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:07 DEBUG sshd[534]: debug1: session_input_channel_req:
session 98 req exec
May 29 14:43:07 DEBUG sshd[534]: debug2: fd 105 setting O_NONBLOCK
May 29 14:43:07 DEBUG sshd[2515]: debug1: permanently_set_uid: 0/0
May 29 14:43:07 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len 0
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: read failed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: close_read
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: input open -> drain
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
delayed efd 107/(0)
May 29 14:43:07 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:07 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:07 DEBUG sshd[534]: debug1: session_by_pid: pid 2515
May 29 14:43:07 DEBUG sshd[534]: debug1: session_exit_message: session
98 channel 98 pid 2515
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: request
exit-status confirm 0
May 29 14:43:07 DEBUG sshd[534]: debug1: session_exit_message: release
channel 98
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: write failed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: close_write
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: output open -> closed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: ibuf empty
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: send eof
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: input drain -> closed
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: send close
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: rcvd close
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: gc: notify user
May 29 14:43:07 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:07 DEBUG sshd[534]: debug1: session_close_by_channel:
channel 98 child 0
May 29 14:43:07 DEBUG sshd[534]: debug1: session_close: session 98 pid 0
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: gc: user detached
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:07 DEBUG sshd[534]: debug2: channel 98: garbage collecting
May 29 14:43:07 DEBUG sshd[534]: debug1: channel 98: free:
server-session, nchannels 99
May 29 14:43:07 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1410 win 30000 max 33976
May 29 14:43:07 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:07 DEBUG sshd[534]: debug1: channel 98: new [server-session]
May 29 14:43:07 DEBUG sshd[534]: debug1: session_new: session 98
May 29 14:43:07 DEBUG sshd[534]: debug1: session_open: channel 98




May 29 14:43:09 DEBUG sshd[534]: debug1: session_open: session 98:
link with channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 98 request exec reply 1
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_input_channel_req:
session 98 req exec
May 29 14:43:09 DEBUG sshd[534]: debug2: fd 105 setting O_NONBLOCK
May 29 14:43:09 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
May 29 14:43:09 DEBUG sshd[2516]: debug1: permanently_set_uid: 0/0
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len 0
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: read failed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: close_read
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: input open -> drain
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
delayed efd 107/(0)
May 29 14:43:09 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:09 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_pid: pid 2516
May 29 14:43:09 DEBUG sshd[534]: debug1: session_exit_message: session
98 channel 98 pid 2516
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: request
exit-status confirm 0
May 29 14:43:09 DEBUG sshd[534]: debug1: session_exit_message: release
channel 98
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: write failed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: close_write
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: output open -> closed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: ibuf empty
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: send eof
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: input drain -> closed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: send close
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: rcvd close
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: gc: notify user
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_close_by_channel:
channel 98 child 0
May 29 14:43:09 DEBUG sshd[534]: debug1: session_close: session 98 pid 0
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: gc: user detached
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: garbage collecting
May 29 14:43:09 DEBUG sshd[534]: debug1: channel 98: free:
server-session, nchanne:q

ls 99
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1411 win 30000 max 33976
May 29 14:43:09 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:09 DEBUG sshd[534]: debug1: channel 98: new [server-session]
May 29 14:43:09 DEBUG sshd[534]: debug1: session_new: session 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_open: channel 98


May 29 14:43:09 DEBUG sshd[534]: debug1: session_open: session 98:
link with channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 98 request exec reply 1
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_input_channel_req:
session 98 req exec
May 29 14:43:09 DEBUG sshd[534]: debug2: fd 105 setting O_NONBLOCK
May 29 14:43:09 DEBUG sshd[2517]: debug1: permanently_set_uid: 0/0
May 29 14:43:09 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len 0
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: read failed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: close_read
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: input open -> drain
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
delayed efd 107/(0)
May 29 14:43:09 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:09 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_pid: pid 2517
May 29 14:43:09 DEBUG sshd[534]: debug1: session_exit_message: session
98 channel 98 pid 2517
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: request
exit-status confirm 0
May 29 14:43:09 DEBUG sshd[534]: debug1: session_exit_message: release
channel 98
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: write failed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: close_write
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: output open -> closed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: ibuf empty
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: send eof
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: input drain -> closed
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: send close
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: rcvd close
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: gc: notify user
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_close_by_channel:
channel 98 child 0
May 29 14:43:09 DEBUG sshd[534]: debug1: session_close: session 98 pid 0
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: gc: user detached
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:09 DEBUG sshd[534]: debug2: channel 98: garbage collecting
May 29 14:43:09 DEBUG sshd[534]: debug1: channel 98: free:
server-session, nchannels 99
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1412 win 30000 max 33976
May 29 14:43:09 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:09 DEBUG sshd[534]: debug1: channel 98: new [server-session]
May 29 14:43:09 DEBUG sshd[534]: debug1: session_new: session 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_open: channel 98



May 29 14:43:09 DEBUG sshd[534]: debug1: session_open: session 98:
link with channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:09 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 98 request exec reply 1
May 29 14:43:09 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:09 DEBUG sshd[534]: debug1: session_input_channel_req:
session 98 req exec
May 29 14:43:09 DEBUG sshd[534]: debug2: fd 105 setting O_NONBLOCK
May 29 14:43:09 DEBUG sshd[2518]: debug1: permanently_set_uid: 0/0
May 29 14:43:09 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len 0
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read failed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_read
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input open -> drain
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
delayed efd 107/(0)
May 29 14:43:10 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:10 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_pid: pid 2518
May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: session
98 channel 98 pid 2518
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: request
exit-status confirm 0
May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: release
channel 98
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: write failed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_write
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: output open -> closed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf empty
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send eof
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input drain -> closed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send close
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: rcvd close
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: gc: notify user
May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:10 DEBUG sshd[534]: debug1: session_close_by_channel:
channel 98 child 0
May 29 14:43:10 DEBUG sshd[534]: debug1: session_close: session 98 pid 0
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: gc: user detached
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: is dead
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: garbage collecting
May 29 14:43:10 DEBUG sshd[534]: debug1: channel 98: free:
server-session, nchannels 99
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1413 win 30000 max 33976
May 29 14:43:10 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:10 DEBUG sshd[534]: debug1: channel 98: new [server-session]
May 29 14:43:10 DEBUG sshd[534]: debug1: session_new: session 98
May 29 14:43:10 DEBUG sshd[534]: debug1: session_open: channel 98



May 29 14:43:10 DEBUG sshd[534]: debug1: session_open: session 98:
link with channel 98
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 98 request exec reply 1
May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_channel: session
98 channel 98
May 29 14:43:10 DEBUG sshd[534]: debug1: session_input_channel_req:
session 98 req exec
May 29 14:43:10 DEBUG sshd[534]: debug2: fd 105 setting O_NONBLOCK
May 29 14:43:10 DEBUG sshd[2519]: debug1: permanently_set_uid: 0/0
May 29 14:43:10 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len 0
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read failed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_read
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input open -> drain
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
delayed efd 107/(0)
May 29 14:43:10 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:10 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_pid: pid 2519
May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: session
98 channel 98 pid 2519
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: request
exit-status confirm 0
May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: release
channel 98
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: write failed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_write
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: output open -> closed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf empty
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send eof
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input drain -> closed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send close
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1414 win 30000 max 33976
May 29 14:43:10 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:10 DEBUG sshd[534]: debug1: channel 99: new [server-session]
May 29 14:43:10 DEBUG sshd[534]: debug1: session_new: session 99
May 29 14:43:10 DEBUG sshd[534]: debug1: session_open: channel 99


May 29 14:43:10 DEBUG sshd[534]: debug1: session_open: session 99:
link with channel 99
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_open:
confirm session
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_req:
channel 99 request exec reply 1
May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_channel: session
99 channel 99
May 29 14:43:10 DEBUG sshd[534]: debug1: session_input_channel_req:
session 99 req exec
May 29 14:43:10 DEBUG sshd[534]: debug2: fd 106 setting O_NONBLOCK
May 29 14:43:10 DEBUG sshd[2520]: debug1: permanently_set_uid: 0/0
May 29 14:43:10 DEBUG sshd[534]: debug2: fd 108 setting O_NONBLOCK
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: read<=0 rfd 106 len 0
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: read failed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: close_read
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: input open -> drain
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: ibuf_empty
delayed efd 108/(0)
May 29 14:43:10 DEBUG sshd[534]: debug2: notify_done: reading
May 29 14:43:10 DEBUG sshd[534]: debug1: Received SIGCHLD.
May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_pid: pid 2520
May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: session
99 channel 99 pid 2520
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: request
exit-status confirm 0
May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: release
channel 99
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: write failed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: close_write
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: output open -> closed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: read 0 from efd 108
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: closing read-efd 108
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: ibuf empty
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: send eof
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: input drain -> closed
May 29 14:43:10 DEBUG sshd[534]: debug2: channel 99: send close
May 29 14:43:10 DEBUG sshd[534]: debug1: server_input_channel_open:
ctype session rchan 1415 win 30000 max 33976
May 29 14:43:10 DEBUG sshd[534]: debug1: input_session_request
May 29 14:43:11 DEBUG sshd[534]: debug2: channel: expanding 110
May 29 14:43:11 DEBUG sshd[534]: debug1: channel 100: new [server-session]
May 29 14:43:11 DEBUG sshd[534]: debug1: session_open: channel 100

--------------no more sessions praseed----------------



May 29 14:43:11 ERR sshd[534]: error: no more sessions
May 29 14:43:11 DEBUG sshd[534]: debug1: session open failed, free channel 100
May 29 14:43:11 DEBUG sshd[534]: debug1: channel 100: free:
server-session, nchannels 101
May 29 14:43:11 DEBUG sshd[534]: debug1: server_input_channel_open:
failure session

Damien Miller

2008-May-30 19:39 UTC

head link

"ERR sshd: error: no more sessions" issue

On Fri, 30 May 2008, Praseed V Gopal wrote:
> Initially send this mail to user group. then realized this is more apt
> place. Apologies for posting in both groups...
> 
> Hi all,
> We're using openssh version 4.7p on our linux 2.6-22 kernel.
> We have a Java based GUI that opens a secure shell connection to this linux
box.
> To do something over the connection, the GUI opens a session (some
> times 3-4 simultaneous sessions) & once done, it will close the
> connection gracefully (I believe).
> The problem is after a few sessions (10) are open & closed, we see
> "May 29 14:43:11 ERR sshd[534]: error: no more sessions" error.
> So I checked the source code of openssh & changed the value of
> MAX_SESSIONS  from 10 to 100.in session.c @ line number 132.
> 
> Things got improved, but now after number of sessions crosses 100, the
> same error pops up.
> I enabled the debug mode. Debug messages are at the end of this mail.
> 
> 1) Please tell me, whether the sessions are getting closed properly?
>  2) If yes, why it is not decrementing the used sessions & reusing the
> already closed sessions?
> 3) is this supposed to work this way?
> 4) How do I fix it or work around this?
It looks like the problem lies with your Java client. Compare the sequence
of a successful session closure:
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len
0
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read failed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_read
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input open -> drain
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
> delayed efd 107/(0)
> May 29 14:43:10 DEBUG sshd[534]: debug2: notify_done: reading
> May 29 14:43:10 DEBUG sshd[534]: debug1: Received SIGCHLD.
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_pid: pid 2518
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: session
> 98 channel 98 pid 2518
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: request
> exit-status confirm 0
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: release
> channel 98
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: write failed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_write
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: output open ->
closed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf empty
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send eof
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input drain ->
closed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send close
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: rcvd close
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: is dead
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: gc: notify user
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_channel: session
> 98 channel 98
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_close_by_channel:
> channel 98 child 0
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_close: session 98 pid 0
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: gc: user detached
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: is dead
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: garbage collecting
> May 29 14:43:10 DEBUG sshd[534]: debug1: channel 98: free:
> server-session, nchannels 99
Broadly speaking, a "channel" is the SSH protocol's abstraction
for a
bidirectional pipe, and a "session" handles command/shell/subsystem
execution. A session uses a channel for communication.

The sequence here is:

1. channel read failed
2. child process exited
3. simulate a channel write failure (the child process is gone by now)
4. send channel eof
5. wait for input to drain (in this case it already has)
6. send channel close
7. *remote* sends a channel close
8. session is detached from channel
9. channel is freed

Here is one that failed to clean up properly.
> May 29 14:43:10 DEBUG sshd[534]: debug2: fd 107 setting O_NONBLOCK
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read<=0 rfd 105 len
0
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read failed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_read
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input open -> drain
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf_empty
> delayed efd 107/(0)
> May 29 14:43:10 DEBUG sshd[534]: debug2: notify_done: reading
> May 29 14:43:10 DEBUG sshd[534]: debug1: Received SIGCHLD.
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_by_pid: pid 2519
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: session
> 98 channel 98 pid 2519
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: request
> exit-status confirm 0
> May 29 14:43:10 DEBUG sshd[534]: debug1: session_exit_message: release
> channel 98
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: write failed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: close_write
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: output open ->
closed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: read 0 from efd 107
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: closing read-efd 107
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: ibuf empty
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send eof
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: input drain ->
closed
> May 29 14:43:10 DEBUG sshd[534]: debug2: channel 98: send close
Here steps 1-6 happened, but the remote end never replied with a channel
close. This means the server cannot continue to detach the session from
the channel and deallocate the channel.

Increasing MAX_SESSIONS will only forestall the inevitable: your client
is not closing channels properly, which causes a session leak on the 
server.

-d

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