You're thinking of SUID - Set UID where a file is owned by one user (e.g. root), has the SUID bit set and then when anyone executes it, it executes with root authority.
It looks like this
-rxsr-xr-x filename
You set it with chmod u+x <filename>
Note that you can set whole filesystems to not run suid binaries, so if it doesn't work, check /etc/fstab for nosuid.
Iain.
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