Linux – Make a process unkillable on Linux

killlinuxprocess

I'm working on a password manager application, and for security reasons I want to launch an unkillable process.

And besides I don't want this program to be a daemon since I need to read from standard input and write to it.

Is there a way to do this?

Best Answer

Make the password manager run under a separate user and handle/ignore/block terminal-generated signals (SIGINT, SIGQUIT, SIGHUP, SIGTSTP, SIGTTIN, and SIGTTOU).

You can't send signals to (=kill) processes run under a different user (user whose both real uid and saved-set uid is different from your effective uid) unless your effective id is 0 (root).

All processes will still be killable by root.

For closer details, see kill(2).

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Linux – Make daemon start up with Linux

You don't modify the /etc/init.d/skeleton file. You copy it to a new file /etc/init.d/mamoudservice (replace mamoudservice with a more suitable name) and then you edit that new file appropriately.

Then you add a symlink from /etc/rc2.d/S99mamoudservice to /etc/init.d/mamoudservice etc.

Use e.g.

   /bin/bash -vx /etc/init.d/mamoudservice start

to understand how the bash shell is interpreting your script.

If your daemon program /usr/sbin/mamouddaemon is coded in C or in C++, I suggest using openlog and syslog inside, at least to get debugging messages (don't output to stderr or stdout in a daemon, it could go nowhere).

An alternative to having your /etc/init.d/mamoudservice script might be to put a @reboot entry in your crontab

Apache – Unkillable apache2 processes

First, check your RAM.

A process that doesn't respond to SIGKILL is a symptom of either a kernel bug or a hardware bug. When you haven't just changed your kernel, the most likely reason is that your RAM is failing, so check it. Kernel bugs can have subtle causes (such as using the wrong version of gcc) and manifest themselves subtly (such as working perfectly except that the X server wouldn't start — same true story). It's not very likely that your new kernel is buggy, if you're using the distribution-provided kernel that a lot of other users are using, but it could happen — possibly a rare bug triggered by a combination of drivers and activity patterns. Try another kernel.

There may also be a bug in Apache that causes it to crash, but if SIGKILL doesn't work, it's not Apache's fault.

Best Answer

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Linux – Make daemon start up with Linux

Apache – Unkillable apache2 processes

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