What is PTY?

A pseudo-terminal (PTY) is a pair of virtual character devices that provide a bidirectional communication channel. One end of the channel is called the master; the other end is called the slave. The slave end of the pseudo-terminal provides an interface that behaves exactly like a classical terminal. A process that expects to be connected to a terminal, can open the slave end of a pseudo-terminal and then be driven by a program that has opened the master end. Anything that is written on the master end is provided to the process on the slave end as though it was input typed on a terminal.

Check maximum number of PTY

Login as root and type the following command

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

Sample output

4096

Increase the maximum number of PTY temporarily

If you need to increase the PTYs to allow more sessions temporarily. Type the following command

[root@lifelinux ~]# echo 5000 > /proc/sys/kernel/pty/max

The setting is changed instantly but this setting will be erased after the reboot.

Increase the maximum number of PTY permanently

Edit kernel configuration file at /etc/sysctl.conf, enter

[root@lifelinux ~]# vi /etc/sysctl.conf

Add or edit following config directive

kernel.pty.max = 5000

To enable the changes made in sysctl.conf you will need to run the command

[root@lifelinux ~]# sysctl -p

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