Pseudo Terminals Limits

"/proc/sys/kernel/pty/max" file defines the maximum number of pseudoterminals,

[root@mail ~]# cat /proc/sys/kernel/pty/max

4096

[root@mail ~]#


"/proc/sys/kernel/pty/nr" is read-only file indicates how many pseudoterminals are currently in use

[root@mail ~]# cat /proc/sys/kernel/pty/nr

4

[root@mail ~]#

To limit or increase the Pseudo Terminals Permanently, 

# vim /etc/sysctl.conf

kernel.pty.max = 1024

#  sysctl -p

After the pty limits you will get below error if you try to open new session,