Kernel parameter npty.

[Joe Short]

I have a client that would like to increase the number of telnet sessions. They are concerned because the system currently has 60 device files in /dev/pty, and npty is set to 60. They want to know if setting the npty parameter to a larger value will:
a.) increase the maximum number of
concurrent telnet sessions?
b.) will additional devices be created in
/dev/pty when the valuse is increased?

[Patrick Wallek]

a) Not necessarily. If this is HP-UX 11.0 or higher then you also need to increase the nstrtel and nstrpty parameters.

b) The additional devices will be created when the system is rebooted as a result of the kernel modification.

[Bill Hassell · Accepted solution]

npty (and nstrtel, nstrpty) provide the needed device files for a network connection, typically a login. If your customer wants to increase the number of telnet sessions, then the answer to a) is obviously yes since that is the desired result. And the answer to b) is also yes+ since you need different device files for the different connection methods. Note that thousands of pty device files occupy no space other than their inodes. /dev is a very small directory (hint: du -ks /dev to see the Kbytes used by the /dev directory)

So you can increase all 3 parameters to 5000 and not worry about having to increase them at a later time. If 5 people login, then 5 pty pairs will be used. HP-UX doesn't care whether 5000 different users login or 5 users each start 1000 sessions each. Note that if 5000 logins are present, there is no additional load on the system. If all the users decide to find / or du / then your system will be crawling very slowly. But a single user could also login and start 5000 processes in the background. The point is that increasing pty values does not 'load' the system -- users load the system by what they are doing.

[Joe Short]

Thank you for the quick and accurate responses.
Happy Holidays everyone.