Beside the root (which I guess IS guaranteed), is there any other username guaranteed to exist on Unix system? Linux system? Fixed UIDs for those users? If not guaraneed, are there at least any recommendations?

My sampling of several Linux distros showed that users such as 'bin', 'daemon', 'sys', 'www-data' and 'nobody' were present, though UIDs differed a bit so that appears to be 'no' on the UID question...

  • If it is a customized system don't count with root either. The important part is the UID (I guess that is what you meant with PID), you can have user pepe with UID=0 and have no root in the system (if you customize your system) and being pepe the user with root privileges (being root actually since his UID is 0). – YoMismo Jan 29 '15 at 16:33
  • yeah, UIDs... fixed in question... – Slartibartfast Jan 29 '15 at 16:53

nothing is guaranteed. root - is usually on linux/unix systems, but - i saw systems where uid=0 was used by "admin".

Usually - there are users like root, nobody, daemon, bin, sys. www-data is on debian/ubuntu, but for example on redhat/centos/fedora/pld there is apache user instead. Recomendations/fixed uids for users other than root are only within distribution.

The same is with uids of regular users - sometimes they start from 100, sometimes from 500, sometimes from 1000...

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