mjhjmtu

I'm trying to:

sudo echo "$USER: my message" > /dev/kmsg

to write a message to the dmesg log. This causes a 'permission denied' error, because it is redirecting the output of 'sudo' (while no longer privileged) to /dev/kmsg. So the 'echo' command is running as root and the writing to /dev/kmsg is running as me. Quoting 'echo' command and ther the redirect ('>/dev/kmsg') doesn't work because the redirection is a shell service that sudo doesn't understand. (The userid in question is in sudoers with NOPASSWD.)

Is there some Linux command that takes the file name as an option and writes its arguments out? Like: 'tee /dev/kmsg -- My message to be logged' I know about the 'logger' command, but that doesn't write to whatever log file 'dmesg' sees. (I want to intersperse some of my messages in with the boot process to know when certain things happen.)

This works, but has the problem of needing to have some place to write a file to:

echo "$USER: My msg" >/tmp/foo
sudo cp /tmp/foo /dev/kmsg
rm /tmp/foo

Solution from ctrl-alt-delor's comment below:

echo "my message" | sudo tee /dev/kmsg >/dev/null

Although it does use piping and redirection, it occurs in the unprivileged shell. Privileged access to '/dev/kmsg' occurs in the 'tee' command in 'sudo'. And it doesn't need write to a disk file (which could have problems).

Also @stolenmoments solution:

echo something | sudo dd of=/dev/kmsg

Putting aside the "why", any command that reads stdin and writes to a named output file will do. My favorite is "dd", but I'm old enough to have used what "dd" refers to.

echo something | sudo dd of=/dev/kmsg

should work just fine.

Use the logger command which is the shell's command-line interface to the syslog system log module. You can use the -p switch to alter which priority the log message is raised with, which in turn is used to determine into which log file the message is written. From the manual:

 -p, --priority priority
 Enter the message into the log with the specified priority. The priority may be specified numerically or as a facility.level pair. For example, -p local3.info logs the message as infor‐
 mational in the local3 facility. The default is user.notice.

I know you asked for something without shell redirection, but you could make your sudo command work by changing it to the following:

sudo su -c 'echo "$USER: my message" > /dev/kmsg'