I am running very simple command: [tester@centos-lvm ~]$ time cal > /dev/null real 0m0.001s user 0m0.000s sys 0m0.001s However, if I specify full path to the `time` executable I get different output: [tester@centos-lvm ~]$ /usr/bin/time cal > /dev/null 0.00user 0.00system 0:00.00elapsed ?%CPU (0avgtext+0avgdata 928maxresident)k 0inputs+0outputs (0major+272minor)pagefaults 0swaps I believe when I run `time` (without path) the `/usr/bin/time` is actually executed: [tester@centos-lvm ~]$ which time /usr/bin/time `man time` tells that there are two different output formats, the `-p` option chooses between them. But I have not specified any options! I checked aliases, nothing there about time. This behavior is quite unexpected and very strange. Could someone explain why and how this happens?