To empty or delete a log file in Linux or Unix, you can use the > or >| operator to redirect an empty file to the log file. This will overwrite the contents of the log file with an empty file, effectively deleting the contents of the log file.
For example, to empty the /var/log/messages log file, you can use the following command:
$ > /var/log/messages
This will overwrite the contents of the /var/log/messages log file with an empty file.
If the log file is currently being written to by another process, you may need to use the >| operator to force the redirection to occur, even if the noclobber shell option is set.
For example:
$ >| /var/log/messages
This will force the redirection to occur, even if the noclobber option is set, and will overwrite the contents of the /var/log/messages log file with an empty file.
Note that emptying or deleting a log file may not permanently remove the contents of the log file. Depending on the system, the log file may be rotated and the contents of the log file may be moved to a backup file or deleted by a log rotation utility. In this case, the contents of the log file may still be recoverable from the backup file or from the file system.
To permanently delete the contents of a log file, you may need to use a secure delete utility such as srm or shred to overwrite the contents of the log file multiple times with random data before deleting it. This will make it much more difficult, if not impossible, to recover the contents of the log file.
For example, to securely delete the /var/log/messages log file using srm, you can use the following command:
$ srm -v /var/log/messages
This will overwrite the contents of the /var/log/messages log file multiple times with random data before deleting it, making it much more difficult, if not impossible, to recover the contents of the log file.