IBM Support

IBM AIX: How to resolve ssh login failure due to running out of ptys

Troubleshooting


Problem

A user fails to log in with ssh into an AIX® system with the error:

PTY allocation request failed on channel 0

Cause

The ssh login failure is caused because the AIX SSH server cannot allocate pty instance to the new ssh connection, as all the available ptys are already being used.

Diagnosing The Problem

Check the maximum number of available ptys on the AIX ssh server. Login to the server console and run command:
# lsattr -l pty0 -E

Check the processes that are using most of the ptys:
# cd /dev/pts
# fuser *

Or you can also check with:
# lsof /dev/pts/*

Resolving The Problem

1. If the output of the above commands shows a specific process using most of the ptys, investigate about
why the specific process is taking up the ptys and work with the appropriate team that owns the process.
2. If all the ptys that are being used are legitimate, increase the maximum number of ptys with "smit pty".

SUPPORT:

If the instructions in this document do not lead to resolution of the problem, follow these instructions to open a case.  The product must be under warranty or have an active and valid support contract.

a.  Document or take screen captures of all symptoms, errors, or messages.

b.  Capture any logs or data relevant to the issue.

c.  Contact IBM to open a case.

   -For electronic support, visit the IBM Support Community:
     https://www.ibm.com/mysupport
   -If you require telephone support, visit this web page:
      https://www.ibm.com/planetwide/

d.  Provide a detailed description of the issue and reference this technote.

e.  Upload all of the details and data to the case.

   -You can attach files to the case in the IBM Support Community, or
   -Upload data to IBM test case server analysis at this URL:

    http://www.ibm.com/support/docview.wss?uid=ibm10733581

f.  Click here to submit feedback for this document.

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Document Information

Modified date:
14 December 2020

UID

ibm16382094

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