Too many PTYs in use

Problem

SSH session to remote systems is hanging:

Jun  3 10:11:52 serv1 sshd[21086]: error: openpty: Not a typewriter
Jun  3 10:11:52 serv1 sshd[21086]: error: session_pty_req: session 0 alloc failed

Solution

There are too many sessions using PTYs:

# ps -ef | awk '{ print $6 }' | grep "pts" | wc -l
60

Where is the maximum supported PTYs is:

# kctune -v nstrpty

Tunable             nstrpty
Description         Maximum number of Streams-based pseudo-terminals
Module              ptm
Current Value       60 [Default]
Value at Next Boot  60 [Default]
Value at Last Boot  60
Default Value       60
Can Change          At Next Boot Only

# ls /dev/pts | egrep -i '^[0-9]' | wc -w
60

Background

There are actually three different types of ptys in HP-UX. You can see them all among the output of lsdev:

Character Block Driver Class
16 -1 ptym ptym
17 -1 ptys ptys
139 -1 telm strtelm
140 -1 tels strtels
156 -1 ptm strptym
157 -1 pts strptys

The telnet connection uses “telnet stream” ptys. The slave side of those appear as /dev/pts/t*. The dtterm and hpterm terminals use “stream” ptys. The slave side of those appear as /dev/pts/[0-9]*. The xterm terminal uses plain old ptys. The slave side of those appear as /dev/ttyp*. Each type of pty has different kernel parameter limits and different device files. Check the kernel parameters and try recreating the device files with insf. ( example: insf -en 120)

Workaround

Create an SSH session without PTY:

$ ssh -T root@serv1 /bin/ksh -i