Linux how many files are open

The reason is that the operating system needs memory to manage each open file, and memory is a limited resource - especially on embedded systems. As root user you can change the maximum of the open files count per process via ulimit -n and per system e. Please note that lsof wc -l sums up a lot of duplicated entries forked processes can share file handles etc. Example: This server has out of max open files, although lsof reports a much larger number:.

A Unix file descriptor is a small int value, returned by functions like open and creat , and passed to read , write , close , and so forth. At least in early versions of Unix, a file descriptor was simply an index into a fixed-size per-process array of structures, where each structure contains information about an open file. If I recall correctly, some early systems limited the size of this table to 20 or so. More modern systems have higher limits, but have kept the same general scheme, largely out of inertia.

Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why is number of open files limited in Linux? Ask Question. Asked 9 years, 6 months ago. Active 2 years, 5 months ago. Viewed k times. Improve this question. Just launch an xterm or any new process and watch the second number go down.

Oh my. There is quite a discrepancy here. So how many open files are there? Is an open file a file that is being used, or is it an open file descriptor? A file descriptor is a data structure used by a program to get a handle on a file, the most well know being 0,1,2 for standard in, standard out, and standard error.

The file-max kernel parameter refers to open file descriptors, and file-nr gives us the current number of open file descriptors. The output has various columns, each representing specific information about the file. Lsof provides us with options that help us filter the output to show only the processes that opened a specific file. We can also filter the output to show the files opened by a specific user. We do this by using the -u flag followed by the username as:.

Suppose we want to view all the files opened by a specific process? For this, we can use the PID of the process to filter the output. Since everything in Linux is a file, we can get the network files such as TCP files or connections. Lsof provides us with a mode to loop the output every few seconds.

This allows you to monitor the files opened by a process or user continuously. Lsof is an incredibly useful utility.