In Linux, you may sometimes find that after deleting a file from a disk, no free space is reclaimed. This is because when a particular file is being used by a running process, the file descriptor is not freed until the process releases it.
Let’s look at what to do when you need to free up disk space after deleting a file on a Linux host. In our example, there is almost no free space left on the partition:
# df -h
Find the 10 largest files in Linux with the command:
# du -ahx / | sort -rh | head -10
For example, you have determined that the largest file you can delete right now is /var/log/mysql/error.log. Delete it:
# rm -rf /var/log/mysql/error.logHowever, the used space is not reclaimed after the file is deleted. The file is simply marked as deleted, but is not actually removed from a disk.
Let’s find out which process is using the deleted file:
# lsof | grep deleted | grep error.log
The mariadb service uses this file. Because this daemon serves multiple production DBs, it cannot be stopped or restarted at this time.
Get the file descriptor of the deleted file by the process ID (PID) you received (4441 in this case):
# ls -l /proc/4441/fd | grep error.logIn this example, 200 is a file descriptor.
To free space on a partition, empty the contents of a file by specifying the process PID and the file descriptor in the command:
# > /proc/4441/fd/200Check for free disk space.
In general, it is better to make it a rule (especially for log files) that it is better to clear the file content rather than delete it:
# truncate -s 0 /var/log/mysql/error.logThe target file will be truncated to zero size without deleting it.