Apache Too many open files (24)

Question

Since there's many answers to this question "Too many open files (24)" and how to solve it just increasing number of allowed open files limit i have not found any suggestion how to check who is using these files.

I'm getting this error:

Fatal error: Uncaught exception 'Exception' with message 'Unknown: open(/var/lib/php/session/sess_375048d5pfne5cu3v0l3sjji04, O_RDWR) failed: Too many open files (24)' in

Also I have restarted my apache process:

$ ps aux | grep apa
84:root      7528  0.0  0.1 102376  4908 ?        Ss   11:11   0:00 /usr/sbin/apache2 -k start
85:www-data  7531  0.0  0.0 101528  2952 ?        S    11:11   0:00 /usr/sbin/apache2 -k start
86:www-data  7532  0.0  0.1 1309308 7168 ?        Sl   11:11   0:00 /usr/sbin/apache2 -k start
87:www-data  7533  0.0  0.1 1309308 7312 ?        Sl   11:11   0:00 /usr/sbin/apache2 -k start
91:vagrant   7748  0.0  0.0   8860   648 pts/0    S+   11:20   0:00 grep --color=auto -in apa

Is there any tool to check who's using these files since my virtual box machine actually is sleeping by htop?

Answer 1

Look into the directory /var/lib/php! You will find a lot of files starting with sess_ there. These files contain the session data of your visitors.

How can you check, who is using these files:

lsof -n|grep -F /var/lib/php/sess_

will give you a process list, which processes are using them.

If you remove these files (rm -vf /var/lib/php/sess_*), all of your current visitors will lose their current session (they need to re-login into your site), but the problem will be solved.

A long-term solution would be to expire your sessions more often. In this question you can find, how can you set up in your php to automatically remove expired session files. On my opinion, setting session.cookie_lifetime to around a half hour and session.gc_maxlifetime a little bit longer (f.e. 35 minutes) is okay.

If you have only a small site with a few visitors (at most some tens daily), it is far enough if you delete the old session files daily from crontab.

If you have a big site, or you want a super user-friendly (but not so secure) site, you need to be able to handle a lot of sessions. On my opinion, in this case it is better if you use some alternate php session solution with a database backend.

The command find /var/lib/php -type f -name "sess_*" \! -ctime 1440|xargs -P 1 -n 50 rm -vf will delete all files in this directory starting with sess_ and older as a day.