ulimit not working, what's the matter?

Question

linux

ulimit -n 1617596
-bash: ulimit: open files: cannot modify limit: Operation not permitted

session required pam_limits.so in /etc/pam.d/common-session registered, changing limits through /etc/security/limits.conf also does not work.
VDS (real server) on Ubuntu 18.04, closed all ssh sessions

Answer 1

Maximum 1048576

Answer 2

1) Under root user?
2) ulimit is a per-user limit, it cannot be greater than kernel limits. Check and increase if necessary fs.nr_open in sysctl ( https://access.redhat.com/solutions/1479623)