OpenSSH ssh-rand-helper - insufficient data

Technote (troubleshooting)


Problem(Abstract)

FOTS1945 ssh-rand-helper child produced:insufficient data

Symptom

When using OpenSSH v1.2.0, intermittent timeouts or a timing conflict may occur.

The error messages include:
FOTS1842 problem renaming PRNG seedfile:from ...
(EDC5112I Resource:temporarily unavailable.
FOTS1945 ssh-rand-helper child produced:insufficient data
FOTS0841 Connection closed


Cause

Timeouts or a timing conflict may occur when running ssh-rand-helper if the commands in the prng_cmds file cannot get enough CPU time to execute. These messages may also occur when the user has multiple jobs running that try to copy the temp seed file to the user's seed file.

This is typically a random event dependent on system workload.


Environment

OpenSSH 1.2

Diagnosing the problem

Refer to the error messages.

Resolving the problem

First, try re-running the job to see if this clears up the problem.

Second, message FOTS1945 can be seen for many issues, but when it is accompanied with the other messages listed above, then continue reading....

If the issue persists and you are running OpenSSH 1.2, you can modify the default 1 second time limit to allow for more time with the use of the _ZOS_SSH_PRNG_CMDS_TIMEOUT environment variable.
The timeout value is in milliseconds and has a minimum value of 1 and a maximum value of
2147483646. The default value is 1000. (This equates to one second). Therefore, increase the amount above 1000.
This env var can be set as an export in the user's .profile. Another option is to place it in a data set so that all users can point to it with a STDENV DD statement in their batch job.
If possible, install ICSF to eliminate the timing window, even if the hardware is not available. It will still implement /dev/random and remove the need to use ssh-rand-helper.

More information about the environment variable can be found in the manual,
IBM Ported Tools for z/OS: OpenSSH User's Guide, on page 9:
http://www-03.ibm.com/systems/resources/fot4os02.pdf

Related information

OpenSSH User's Guide

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Document information


More support for:

z/OS family

Software version:

1.12, 1.13, 2.1

Operating system(s):

z/OS

Reference #:

T1019539

Modified date:

2014-05-21

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