Only kill -9 will works, other signals have been caught up.
kenchow@ken-U64:~/Documents/git-test$ ./signal & [1] 3942 kenchow@ken-U64:~/Documents/git-test$ kill -1 3942 Catch signal = 1 kenchow@ken-U64:~/Documents/git-test$ kill -2 3942 Catch signal = 2 kenchow@ken-U64:~/Documents/git-test$ kenchow@ken-U64:~/Documents/git-test$ kill -3 3942 Catch signal = 3 kenchow@ken-U64:~/Documents/git-test$ kill -4 3942 Catch signal = 4 kenchow@ken-U64:~/Documents/git-test$ kill -5 3942 Catch signal = 5 kenchow@ken-U64:~/Documents/git-test$ kill -6 3942 Catch signal = 6 kenchow@ken-U64:~/Documents/git-test$ kenchow@ken-U64:~/Documents/git-test$ kill -1 3942 Catch signal = 1 kenchow@ken-U64:~/Documents/git-test$ kill -2 3942 Catch signal = 2 kenchow@ken-U64:~/Documents/git-test$ kill -3 3942 Catch signal = 3 kenchow@ken-U64:~/Documents/git-test$ kill -4 3942 Catch signal = 4 kenchow@ken-U64:~/Documents/git-test$ kill -5 3942 Catch signal = 5 kenchow@ken-U64:~/Documents/git-test$ kill -6 3942 Catch signal = 6 kenchow@ken-U64:~/Documents/git-test$ kill -7 3942 Catch signal = 7 kenchow@ken-U64:~/Documents/git-test$ kill -8 3942 Catch signal = 8 kenchow@ken-U64:~/Documents/git-test$ kill -9 3942 [1]+ Killed ./signal kenchow@ken-U64:~/Documents/git-test$ ./signal & [1] 4018 kenchow@ken-U64:~/Documents/git-test$ kill -10 4018 Catch signal = 10 kenchow@ken-U64:~/Documents/git-test$ kill -11 4018 Catch signal = 11 kenchow@ken-U64:~/Documents/git-test$ kill -12 4018 Catch signal = 12 kenchow@ken-U64:~/Documents/git-test$ kill -13 4018 Catch signal = 13 kenchow@ken-U64:~/Documents/git-test$ kill -14 4018 Catch signal = 14 kenchow@ken-U64:~/Documents/git-test$ kill -99 4018 -bash: kill: 99: invalid signal specification kenchow@ken-U64:~/Documents/git-test$ kill -100 4018 -bash: kill: 100: invalid signal specification kenchow@ken-U64:~/Documents/git-test$ kill -15 4018 Catch signal = 15