determine ulimit for root user

Get the PID of the process that solr is running and then cat /proc/$SOLR_PID/limits -- this will tell you the actual limits of the process.

I'd recommend to run things like solr as a seperated unprivileged user. When doing this you have multiple options (limits.conf or add a ulimit -n 2048 to the init script, ...). The last one isn't all that shiny but works for quick settings and restarting the daemon

RANT: don't tell me you can't restart becauso you'll lose service. If that is the case you should have a HA setup anyway :)

After changing number of open files in /etc/security/limits.conf, user must log out and log back in to take effect. So, try this:

$ sudo su -
# ulimit -Sn

I know this question has an answer, but that looks more like a work around, not a real solution.

According to ubuntu this is not a bug but a documentation issue, see: https://bugs.launchpad.net/ubuntu/+source/pam/+bug/65244

Thanks for your report. As you said this is not a bug in pam but a documentation issue. The fact to allow explicitly allow limits for user root has been addressed a while ago (30 Aug 2000) but you need to explicitly name user root to apply the limits.

So if you want to change the ulimit on all users, including the root user you have to specify:

*         -    nofile            2048
root      -    nofile            2048