“The system resource RLIMIT_NOFILE is set at an unusually low level for IBM MQ”

I had this problem, and fixed it, and now I’ve upgraded to Ubuntu 20.04 it has come back again.

There are various hints like IBM Support telling me to change /etc/security/limits.conf, but these did not solve the problem for me.

I understand the words below, but not the overall picture. If you get this problem – and the standard changes do not work – try the /etc/systemd/user.conf change as well.

Changes to /etc/security/limits.conf apply to non GUI command windows and limits.conf is not used when systemd is running.

Recent changes to systemd include

• The Linux kernel’s current default RLIMIT_NOFILE resource limit for userspace processes is set to 1024 (soft) and 4096 (hard). Previously, systemd passed this on unmodified to all processes it forked off. With this systemd release the hard limit systemd passes on is increased to 512K, overriding the kernel’s defaults and substantially increasing the number of simultaneous file descriptors unprivileged userspace processes can allocate …

For graphical login.  command windows (such as GNOME on Linux) you need.. (I’m copying)

Add the following line to /etc/systemd/user.conf:

DefaultLimitNOFILE=65535

That change works, but only affecting the soft limit. (Leaving us capped with a hard limit of 4096 still.) In order to affect the hard limit, we must modify /etc/systemd/system.conf with the same changes.