How to empty the content of a log file

Question

I have a process which is continuously writing into a log file. I want to empty the contents of the log file without having to restart the process.

I have used various commands:

: > log.txt
echo "" > log.txt
truncate -s 0 log.txt
cat /dev/null > log.txt

They all truncate/empty the content of the log file but only temporarily. When a few minutes later process updates the content, log file size (and contents) goes back to (and newer content) what it originally was.

what might be going on and how I can permanently empty the log file contents ?

log file for the running process cannot be changed. I want to rotate the logs at mid-night every day without having to restart the process which cant auto-rotate the log files. So previous days log file is are archived and log file is emptied to be filled again until next mid-night. — tanatan
– tanatan, Commented Aug 12, 2021 at 11:37

koyaanisqatsi · Accepted Answer · 2021-08-12 11:22:01Z

1

For me a permanently empty log is done with simply link it to the black hole named: /dev/null
So try it (as root) by yourself with: rm log.txt && ln -sfv /dev/null log.txt

Thats not only for security reason.
On a Raspberry Pi or embedded devices it makes the Memory Card living much longer.

Unwanted history files i link in this way for security reason...

# ls -lah .*history
lrwxrwxrwx 1 root root 9 Aug  6  2020 .ash_history -> /dev/null
lrwxrwxrwx 1 root root 9 Jun 12  2020 .bash_history -> /dev/null

...so every session starts with an empty one.

edited Aug 12, 2021 at 11:22

answered Aug 12, 2021 at 10:55

koyaanisqatsi

2,9052 gold badges11 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

tanatan Over a year ago

Sorry this is not what I want to achieve. I want to rotate the logs at mid-night every day without having to restart the process which cant auto-rotate the log files. So previous days log file is are archived and log file is emptied to be filled again until next mid-night.

Léa Gris Over a year ago

@tanatan You really should look into the logrotate command and its man-page man7.org/linux/man-pages/man8/logrotate.8.html

tanatan Over a year ago

thanks @LéaGris. Had a quick look but not sure how this will fix the issue I am facing "The commands truncate/empty the content of the log file but only until process adds more logs to the log file. When a few minutes later process updates the log file, log file size goes back to what it originally was. I am not sure how the old content comes back in the log file when I had just emptied is using one of the command."

Collectives™ on Stack Overflow

How to empty the content of a log file

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related