Posted on March 16, 2023 by darshin
This tutorial explains how to truncate files to zero size in Linux systems using shell redirection and the
In some situations, you might want to truncate (empty) an existing file to a zero-length. In simple words, truncating a file means removing the file contents without deleting the file.
Truncating a file is much faster and easier than deleting the file , recreating it, and setting the correct permissions and ownership . Also, if the file is opened by a process, removing the file may cause the program that uses it to malfunction.
The easiest and most used method to truncate files is to use the
> shell redirection operator.
The general format for truncating files using redirection is:
: > filename
Let’s break down the command:
trueand produces no output.
The redirection operator
>redirect the output of the preceding command to the given file.
filename, the file you want to truncate.
If the file exists , it will be truncated to zero. Otherwise, the file will be created.
: can also use another command that produces no output.
Here is an example of using the
cat command to output the contents of the
/dev/null device, which returns only an end-of-file character:
cat /dev/null > filename
Another command that can be used is
echo . The
-n option tells
echo not to append a newline:
echo -n > filename
On most modern shells such as Bash or Zsh you can omit the command before the redirection symbol and use:
To be able to truncate a file, you need to have write permissions on the file. Usually, you would use
sudo for this, but the elevated root privileges do not apply to the redirection. Here is an example:
sudo : > /var/log/syslog
bash: /var/log/syslog: Permission denied
There are several solutions that allow redirecting with
sudo. The first option can run a new shell with sudo and execute a command inside that shell using the
sudo sh -c '> filename'
Another option is to pipe the output to the
tee command, elevate the
tee privileges with
sudo, and write the empty output to a given file:
: | sudo tee filename
truncate is a command-line utility that allows you to shrink or extend the size of a file to a given size.
The general syntax for truncating files to zero size with the
truncate command, is as follows:
truncate -s 0 filename
-s 0 option sets the file size to zero.
For example, to empty the Nginx access log you would use:
sudo truncate -s 0 /var/log/nginx/access.log
Empty All Log Files
Over time, your disk drive may get cluttered with a lot of large log files taking up large amounts of disk space.
The following command will empty files ending with “.log” under the
sudo truncate -s 0 /var/log/**/*.log
A better option would be to rotate, compress, and remove the logs files with the
To truncate a file in Linux use the redirection operator
> followed by the file name.
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