'Resource temporarily unavailable' while trying to login or su as a local user in Red Hat Enterprise Linux

Environment

Red Hat Enterprise Linux 4, 5, 6, 7 and 8

Issue

Getting the error below while trying to tát su or to tát login as a local user.

su: cannot mix user id:Resource temporarily unavailable

su: failed to tát execute /bin/bash: Resource temporarily unavailable

This error is also observed when logging in as a user on the console and using the SSH.

Resolution

Check /etc/security/limits.conf and all files in /etc/security/limits.d/ for the current setting of the nproc value
Extend the nproc value. This can be done in /etc/security/limits.conf or in any tệp tin in a tệp tin in /etc/security/limits.d/.

Example of /etc/security/limits.conf:

      -      nproc          

e.g.
testuser         -      nproc          10240

In Red Hat Enterprise Linux 6, there's a mặc định setting in /etc/security/limits.d/90-nproc.conf. Change the mặc định limit for all users or add a new limit for the affected user.

# Default limit for number of user's processes to tát prevent
# accidental fork bombs.
# See rhbz #432903 for reasoning.

*          soft    nproc     1024
testuser   soft    nproc     10240    <== add

Root Cause

The user fails to tát log in because an EAGAIN error occurs if the user's number of executing threads has reached the nproc resource limit. Note: Despite the name, this is a limit on threads, not processes.
This error may occur if user's nproc limit is mix to tát /etc/security/limits.conf.
In Red Hat Enterprise Linux 6, this error occurs even if the limit is not explicitly mix because the mặc định configuration for all users is mix in /etc/security/limits.d/90-nproc.conf.

Diagnostic Steps

Check nproc and nofile in /etc/security/limits.conf for the user.
Log in as this user and run rẩy ulimit -u:
```
$ ulimit -u
120831
```

Look at /proc/sys/kernel/threads-max:

# cát /proc/sys/kernel/threads-max
241663

Look at the number of user processes(threads)
```
# ps -u testuser -L | wc -l
103
```

Look at /var/log/secure:

su: pam_keyinit(su-l:session): Unable to tát change UID to tát 24074 temporarily 
su: pam_keyinit(su-l:session): Unable to tát change UID to tát 24074 temporarily

Look at strace. Run strace -ttTvfo /tmp/su.strace su - testuser:

23318 10:35:59.758440 setgid(24075)     = 0 <0.000005>
23318 10:35:59.758471 setuid(24074)     = -1 EAGAIN (Resource temporarily unavailable) <0.000018>

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