How to Check and Increase Linux Open File Limits

Check Linux open file limits

System-wide maximum number of file descriptors is stored in /proc/sys/fs/file-max:

# cat /proc/sys/fs/file-max
365004

Per‑process limits are shown by ulimit. The hard limit ( -Hn) is the maximum value that can be set, while the soft limit ( -Sn) is the current effective limit:

# ulimit -Hn
65535
# ulimit -Sn
65535

To view another user's limits, switch to that user with su and run the same commands:

# su rumenz
$ ulimit -Sn
1024
$ ulimit -Hn
1024

System‑wide file descriptor limit

Server applications (e.g., MySQL/MariaDB, Apache) often require higher limits. Increase the kernel parameter fs.file-max with sysctl: # sysctl -w fs.file-max=500000 Verify the new value: # cat /proc/sys/fs/file-max Changes made with sysctl -w are temporary. To make them permanent, add the line to /etc/sysctl.conf and reload:

# vi /etc/sysctl.conf
fs.file-max=500000
# sysctl -p

User‑level open file limits

Per‑user limits are configured in /etc/security/limits.conf using the format:

<domain>    <type>  <item>  <value>

Example for user rumenz:

# Hard limit for maximum opened files
rumenz    hard    nofile    4096
# Soft limit for maximum opened files
rumenz    soft    nofile    1024

After editing, the user must log out and back in for the new limits to take effect. System‑wide changes can be applied immediately with sysctl -p.