Possible SSH PAM PTY allocation issue -


i have linux ubuntu server hosted on amazon ec2. there around 3000+ linux users created on system userid user_1, user_2 & on.

surprisingly users till user_2685 able login via ssh server. not beyond that.

i have changed loglevel debug3 in /etc/ssh/sshd_config . pasting relevant content.

  1. relevant dump when user fails login - http://pastebin.com/ns2jc8vg
 apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug1: allocating pty. apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug3: mm_request_send entering: type 26 apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug3: mm_pty_allocate: waiting monitor_ans_pty apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug3: mm_request_receive_expect entering: type 27 apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug3: mm_request_receive entering apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug3: mm_request_receive entering apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug3: monitor_read: checking request 26 apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug3: mm_answer_pty entering apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug2: session_new: allocate (allocated 0 max 10) apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug3: session_unused: session id 0 unused apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug1: session_new: session 0 apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18802]: debug1: selinux support disabled apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug1: do_cleanup apr 18 10:18:00 domu-12-31-39-01-86-0c sshd[18879]: debug3: pam: sshpam_thread_cleanup entering
  1. relevant dump when user login - http://pastebin.com/vuxnpdsr
 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: allocating pty. apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug3: mm_request_send entering: type 26 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug3: mm_pty_allocate: waiting monitor_ans_pty apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug3: mm_request_receive_expect entering: type 27 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug3: mm_request_receive entering apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug3: mm_request_receive entering apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug3: monitor_read: checking request 26 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug3: mm_answer_pty entering apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug2: session_new: allocate (allocated 0 max 10) apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug3: session_unused: session id 0 unused apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug1: session_new: session 0 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug1: selinux support disabled apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug3: mm_request_send entering: type 27 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18880]: debug3: mm_answer_pty: tty /dev/pts/37 ptyfd 4 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: session_pty_req: session 0 alloc /dev/pts/37 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: ignoring unsupported tty mode opcode 11 (0xb) apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: ignoring unsupported tty mode opcode 17 (0x11) apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: server_input_channel_req: channel 0 request shell reply 1 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: session_by_channel: session 0 channel 0 apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug1: session_input_channel_req: session 0 req shell apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug2: fd 3 setting tcp_nodelay apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug2: channel 0: rfd 9 isatty apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug2: fd 9 setting o_nonblock apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18957]: debug3: fd 7 o_nonblock apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18958]: debug1: setting controlling tty using tiocsctty. apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18958]: debug3: copy environment: path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games apr 18 10:20:07 domu-12-31-39-01-86-0c sshd[18958]: debug3: copy environment: lang=en_us.utf-8 apr 18 10:20:07 domu-12-31-39-01-86-0c jk_chrootsh[18958]: entering jail /opt/users-rails-apps user user_1 (1001) arguments

update 1:

the above dumps /var/log/auth.log on server. below dumps on client. putting relevant part of dump differs

successful login

 debug2: channel 0: request shell confirm 1 debug2: callback done debug2: channel 0: open confirm rwindow 0 rmax 32768 debug2: channel_input_status_confirm: type 99 id 0 debug2: pty allocation request accepted on channel 0 debug2: channel 0: rcvd adjust 2097152 debug2: channel_input_status_confirm: type 99 id 0 debug2: shell request accepted on channel 0

unsuccessful login

 debug2: channel 0: request shell confirm 1 debug2: callback done debug2: channel 0: open confirm rwindow 0 rmax 32768 debug1: channel 0: free: client-session, nchannels 1 debug3: channel 0: status: following connections open:   #0 client-session (t4 r0 i0/0 o0/0 fd 4/5 cc -1)  connection www.codelearn.org closed remote host. connection www.codelearn.org closed. transferred: sent 2488, received 1472 bytes, in 0.8 seconds bytes per second: sent 3043.4, received 1800.6 debug1: exit status -1

os : ubuntu precise 12.04

openssh server: openssh_5.9p1 debian-5ubuntu1.1, openssl 1.0.1 14 mar 2012

ssh client: not matter have tried ubuntu mac & behavior same.

update 2:

btw - not problem pam such can su user_3000 & new user logs in & gets pty too.

also doing ssh without asking pty ssh -t user_3000@www.codelearn.org logs user in. stops post login & no prompt appears. because no prompt asked @ first place.

have checked sshd_config ensure no maxing out issues occurring?

lookout clientalivecountmax maxsessions maxstartups

specifically maxsessions since unsuccessful login message lists bunch of open connections reason. increase number , check behavior.

you can read more here - http://www.manpagez.com/man/5/sshd_config/


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