How to redirect output of a running program to /dev/null

io-redirection

I know that in order to suppress the output of a program I can redirect it to /dev/null, for example to hide all error and warning messages from chromium I can start the program like this

chromium-browser 2> /dev/null &

However, if I happen to forget about the error messages and type

chromium-browser &

(which is quite annoying when they appear in the middle of a command) I don't know what to do except for stopping the application and starting it again properly.

Can I somehow redirect error output without restarting the application?

Best Answer

You can also launch the browser with nohup and then close the terminal window with the following:

nohup chromium-browser &

This way, the browser will launch and detach from the console, that can then be closed quietly.

Related Solutions

Linux Bash – How to Change Output Redirection of a Running Process

You can do it using reredirect (https://github.com/jerome-pouiller/reredirect/).

reredirect -m /dev/null <PID>

You can restore initial output of your process later using something like:

reredirect -N -O <M> -E <N> <PID>

(<M> and <N> are provided by previous launch of reredirect).

reredirect README also explains how to redirect to another command or to redirect only stdout or stderr.

Cronjob – How to Completely Silence a Cronjob to /dev/null?

Make the line this:

* * * * *       root    /usr/local/sbin/mycommand.sh > /dev/null 2>&1

This will capture both STDOUT (1) and STDERR (2) and send them to /dev/null.

MAILTO

You can also disable the email by setting and then resetting the MAILTO="" which will disable the sending of any emails.

Example

MAILTO=""
* * * * *       root    /usr/local/sbin/mycommand.sh > /dev/null 2>&1

MAILTO="admin@somedom.com"
 * * * * *      root    /usr/local/sbin/myothercommand.sh

Additional messaging

Often times you'll get the following types of messages in /var/log/syslog:

Nov 11 08:17:01 manny CRON[28381]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)

These are simply notifications via cron that a directory of cronjobs was executed. This message has nothing to do directly with these jobs, instead it's coming from the crond daemon directly. There isn't really anything you can do about these, and I would encourage you to not disable these, since they're likely the only window you have into the goings on of crond via the logs.

If they're very annoying to you, you can always direct them to an alternative log file to get them out of your /var/log/syslog file, through the /etc/syslog.conf configuration file for syslog.