The setuid bit on programs

When a program with the setuid bit set is run, it runs with an 'effective' uid of the owner of the file

        # cp /usr/bin/id ./setxid
        # ls -l setxid
        -rwxr-xr-x    1 root     root        13052 Apr 19  4:43 setxid

        # chmod u+s setxid
        # ls -l setxid
        -rwsr-xr-x    1 root     root        13052 Apr 19  4:43 setxid

        $ /usr/bin/id
        uid=1010(bri) gid=1010(bri) groups=1010(bri)

        $ ./setxid
        uid=1010(bri) gid=1010(bri) euid=0(root) groups=1010(bri)