Open file number linux

Linux / UNIX List Open Files for Process

H ow do I list all open files for a Linux or UNIX process using command line options? How can I show open files per process under Linux?

Both Linux and Unix-like operating systems come with various utilities to find out open files associated with the process.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	None
Est. reading time	3 minutes

UNIX List Open Files For Process

First use the ps command command to get PID of process, enter:
$ ps -aef | grep $ ps -aef | grep httpd
Next pass this PID to pfiles command under Solaris Unix:
$ pfiles
$ pfiles 3533
See pfiles command documentation> for more information or type the following man command:
% man pfiles

FreeBSD list open files per process

On FreeBSD use the fstat command along with the ps command:
# ps aux | grep -i openvpn # filter outputs using the grep command #
# fstat -p
# fstat -p 1219
We can count open files count for openvpn process as follows using the wc command:
# fstat -p 1219 | grep -v ^USER | wc -l
The -p option passed to the fstat to report all files open by the specified process.

FreeBSD pstat command in action

Linux List Open Files For Process

First you need to find out PID of process. Simply use any one of the following command to obtain process id:
# ps aux | grep OR
$ ps -C -o pid=
For example, find out PID of firefox web-browser, enter:
$ ps -C firefox -o pid=
Output:

To list opne files for firefox process, enter:
$ ls -l /proc/7857/fd
Sample output:

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For privileged process use the sudo command and to count open files use the wc command on Linux as follows:
# Get process pid
sudo ps -C Xorg -o pid
sudo ls -l /proc/$/fd
# Say pid is 9497 for Xorg, then
sudo ls -l /proc/9497/fd | wc -l
We can use bash for loop as follows too:

Listing Open Files on Linux

Using lsof to display the processes using the most file handles

The lsof command list open files under all Linux distributions or UNIX-like operating system. Type the following command to list open file for process ID 351:
$ lsof -p 351
In this example display and count all open files for top 10 processes on Linux operating systems or server:
# lsof | awk ‘‘ | sort | uniq -c | sort -r | head
## force numeric sort by passing the ‘-n’ option to the sort ##
# lsof | awk ‘‘ | sort | uniq -c | sort -r -n | head

• lsof – Run the lsof to display all open files and send output to the awk
• awk ‘‘ – Display first field i.e. process name only
• uniq -c – Omit duplicate lines while prefix lines by the number of occurrences
• sort -r – Reverse sort
• head – Display top 10 process along with open files count

Conclusion

Now you know how to find open files per process on Linux, FreeBSD, and Unix-like systems using various command-line options. See how to increase the system-wide/user-wide number of available (open) file handles on Linux for more information.

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How to Increase Number of Open Files Limit in Linux

In Linux, you can change the maximum amount of open files. You may modify this number by using the ulimit command. It grants you the ability to control the resources available for the shell or process started by it.

In this short tutorial we will show you how to check your current limit of open files and files descriptions, but to do so, you will need to have root access to your system.

First, Lets see how we can find out the maximum number of opened file descriptors on your Linux system.

Find Linux Open File Limit

The value is stored in:

The number you will see, shows the number of files that a user can have opened per login session. The result might be different depending on your system.

For example on a CentOS server of mine, the limit was set to 818354, while on Ubuntu server that I run at home the default limit was set to 176772.

If you want to see the hard and soft limits, you can use the following commands:

Check Hard Limit in Linux

Check Soft Limits in Linux

To see the hard and soft values for different users, you can simply switch user with “su” to the user which limits you want to check.

How to Check System wide File Descriptors Limits in Linux

If you are running a server, some of your applications may require higher limits for opened file descriptors. A good example for such are MySQL/MariaDB services or Apache web server.

You can increase the limit of opened files in Linux by editing the kernel directive fs.file-max . For that purpose, you can use the sysctl utility.

For example, to increase open file limit to 500000, you can use the following command as root:

You can check the current value for opened files with the following command:

With the above command the changes you have made will only remain active until the next reboot. If you wish to apply them permanently, you will have to edit the following file:

Add the following line:

Of course, you can change the number per your needs. To verify the changes again use:

Users will need to logout and login again for the changes to take effect. If you want to apply the limit immediately, you can use the following command:

Set User Level Open File limits in Linux

The above examples, showed how to set global limits, but you may want to apply limits per user basis. For that purpose, as user root, you will need to edit the following file:

If you are a Linux administrator, I suggest you that you become very familiar with that file and what you can do to it. Read all of the comments in it as it provides great flexibility in terms of managing system resources by limiting users/groups on different levels.

The lines that you should add take the following parameters:

Here is an example of setting a soft and hard limits for user marin:

Final thoughts

This brief article showed you a basic example of how you can check and configure global and user level limits for maximum number of opened files.

While we just scratched the surface, I highly encourage you to have a more detailed look and read regarding /etc/sysctl.conf and /etc/security/limits.conf and learn how to use them. They will be of great help for you one day.

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Linux: Find Out How Many File Descriptors Are Being Used

W hile administrating a box, you may wanted to find out what a processes is doing and find out how many file descriptors (fd) are being used. You will surprised to find out that process does open all sort of files:
=> Actual log file

=> Library files /lib /lib64

=> Executables and other programs etc

In this quick post, I will explain how to to count how many file descriptors are currently in use on your Linux server system.

Step # 1 Find Out PID

To find out PID for mysqld process, enter:
# ps aux | grep mysqld
OR
# pidof mysqld
Output:

Step # 2 List File Opened By a PID # 28290

Use the lsof command or /proc/$PID/ file system to display open fds (file descriptors), run:
# lsof -p 28290
# lsof -a -p 28290
OR
# cd /proc/28290/fd
# ls -l | less
You can count open file, enter:
# ls -l | wc -l

Tip: Count All Open File Handles

To count the number of open file handles of any sort, type the following command:
# lsof | wc -l
Sample outputs:

List File Descriptors in Kernel Memory

Type the following command:
# sysctl fs.file-nr
Sample outputs:

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1. 1020 The number of allocated file handles.
2. 0 The number of unused-but-allocated file handles.
3. 70000 The system-wide maximum number of file handles.

You can use the following to find out or set the system-wide maximum number of file handles:
# sysctl fs.file-max
Sample outputs:

More about /proc/PID/file & procfs File System

/proc (or procfs) is a pseudo-file system that it is dynamically generated after each reboot. It is used to access kernel information. procfs is also used by Solaris, BSD, AIX and other UNIX like operating systems. Now, you know how many file descriptors are being used by a process. You will find more interesting stuff in /proc/$PID/file directory:

• /proc/PID/cmdline : process arguments
• /proc/PID/cwd : process current working directory (symlink)
• /proc/PID/exe : path to actual process executable file (symlink)
• /proc/PID/environ : environment used by process
• /proc/PID/root : the root path as seen by the process. For most processes this will be a link to / unless the process is running in a chroot jail.
• /proc/PID/status : basic information about a process including its run state and memory usage.
• /proc/PID/task : hard links to any tasks that have been started by this (the parent) process.

See also: /proc related FAQ/Tips

/proc is an essentials file system for sys-admin work. Just browser through our previous article to get more information about /proc file system:

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What are the number of open files for a user on linux and system wide for linux? [closed]

Want to improve this question? Update the question so it’s on-topic for Stack Overflow.

Closed 7 years ago .

Sorry, this question has several layers but all deal with the number of open files.

I’m getting a «Too many open files» message in my application log for the app we’re developing. Someone suggested to me to:

1. Find the number of open files currently being used, system wide and per user
2. Find what the limit for open files of the system and user are.

I ran ulimit -n and it returned 1024. I also looked at /etc/limits.conf and there isn’t anything special in that file. /etc/sysctl.conf is also not modified. I’ll list the contents of the files below. I also ran lsof | wc -l , which returned 5000+ lines (if I’m using it correctly).

So, my main questions are:

1. How do I find the number of open files allowed per user? Is the soft limit the nofile setting found/defined in /etc/limits.conf? What is the default since I didn’t touch /etc/limits.conf?
2. How do I find the number of open files allowed system-wide? Is it the hard limit in limits.conf? What’s the default number if limits.conf isn’t modified?
3. What is the number that ulimit returns for open files? It says 1024 but when I run lsof and count the lines, it’s over 5000+ so something is not clicking with me. Are there other cmds I should run or files to look at to get these limits? Thanks in advance for your help.

Content of limits.conf

Content of sysctl.conf

1 Answer 1

There is no per-user file limit. The ones you need to be aware of are system-wide and per-process. The files-per-process limit multiplied by the processes-per-user limit could theoretically provide a files-per-user limit, but with normal values the product would be so large as to be effectively unlimited.

Also, the original purpose of lsof was to LiSt Open Files, but it has grown and lists other things now, like cwd and mmap regions, which is another reason for it to output more lines than you expect.

The error message «Too many open files» is associated with errno value EMFILE , the per-process limit, which in your case appears to be 1024. If you can find the right options to limit lsof to just displaying actual file descriptors of a single process, you’ll probably find that there are 1024 of them, or something very close.

The system-wide file descriptor limit rarely needs to be manually adjusted these days, since its default value is proportional to memory. If you need to, you can find it at /proc/sys/fs/file-max and information about current usage at /proc/sys/fs/file-nr . Your sysctl file has a value of 4096 for file-max , but it’s commented out so you shouldn’t take it seriously.

If you ever manage to hit the system-wide limit, you’ll get errno ENFILE , which translates to the error message «File table overflow» or «Too many open files in system».

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