How to check file descriptors on Linux

README.md

system wide

> cat /proc/sys/fs/file-max
13032310

> cat /proc/sys/fs/file-nr
25696   0       13032310

process wide

> cat /proc/3898/limits | grep "open files"
Max open files            1024                 4096                 files

// can also use ulimit
> ulimit -Hn // hard limit         
4096
> ulimit -Sn // soft limit         
1024  

// number of file descriptors in use
ls /proc/3898/fd/ | wc -l
6

Sometimes you tune the parameter per process using sysctl. That is normal because some process are expecting to use more file descriptors.

// conf
[Service]
LimitNOFILE=65536

cat /proc/5054/limits | grep "open files"
Max open files            65536                65536                files