Getting a unique id from a unix-like system

Question

I want to get from any Unix-like system (if this is possible) a unique id that will be persistent every time my application runs in the same machine. If it is possible, I wa

Answer 1

You can use a lockfile in places like:

• /var/run/yourapp.pid (if program run by root)
• $HOME/.yourapp.pid (if run by user and local filesystem)
• $HOME/.yourapp.$(hostname -f).pid (home on nfs)

When your program is run, it shall do something like:

lock = open(filename, O_CREAT | O_EXCL);
dprintf(lock, "%u", getpid());

If the open fails, check if the process is still running and if not: delete the file and try again.