% id
uid=502(macks) gid=502(macks) groups=502(macks), 80(admin)
% sudo -s
Password:
# id
uid=0(root) gid=0(wheel) groups=0(wheel), 1(daemon), 2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest), 80(admin), 262(distcc)
# ls -ld
drwxr-xr-x  42 macks  macks  1428 14 Jun 19:46 ./
# touch foofoo
# ls -l foofoo
-rw-------  1 root  macks  0 14 Jun 19:50 foofoo
# sudo -u nobody -s
% id
uid=4294967294(nobody) gid=4294967294(nobody) groups=4294967294(nobody)
% cd /tmp
% ls -ld
drwxrwxrwt  12 root  wheel  408 14 Jun 19:45 .
% touch foofoo
% ls -l foofoo
-rw-r--r--  1 nobody  wheel  0 14 Jun 19:50 foofoo
% exit
# cd ~altuser
% ls -ld
drwxr-xr-x  16 altuser  altuser  544 14 Jun 19:46 .
# touch foofoo
# ls -l foofoo
-rw-------  1 root  altuser  0 14 Jun 19:52 foofoo