Month: September 2012

If you want reboot you Linux box and the reboot, init 6 etc. and these commands do not work for you, or you just want to reboot the system in the very, very fast way, type:

echo b > /proc/sysrq-trigger

This is equivalent to the key combination Alt + SysRq + B which reboots the machine. (Immediately reboot the system, without unmounting or syncing filesystems).

kill – sends a signal to a process.

For the list of available signals, type:

kill -l

Sample outputs:

1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL
5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE
9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2
13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGSTKFLT
17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU
25) SIGXFSZ 26) SIGVTALRM 27) SIGPROF 28) SIGWINCH
29) SIGIO 30) SIGPWR 31) SIGSYS 34) SIGRTMIN
35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3 38) SIGRTMIN+4
39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12
47) SIGRTMIN+13 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14
51) SIGRTMAX-13 52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10
55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7 58) SIGRTMAX-6
59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX

SIGHUP (1) – Hangup detected on controlling terminal or death of controlling process.
SIGINT (2) – Interrupt from keyboard.
SIGQUIT (3) – Quit from keyboard (Ctrl-. or, Ctrl-4 or, on the virtual console, the SysRq key)
SIGILL (4) – Terminate the process and dump core.
SIGABRT (6) – Abort signal from abort(3) – software generated.
SIGFPE (8) – Floating point exception.
SIGKILL (9) – Kill signal, kill running process.
SIGTERM (15) – Termination signal.
SIGCONT (18) – Continue process if stopped.
SIGSTOP (19) – Stop process.
SIGSTP (20) – Stop typed at tty (CTRL+z) .

Julia this is for you:-)

| command1 | command2
Linux shell pipes join the standard output of command1 to the standard input of command2. Output of the ps command is provided as the standard input to the grep command.
ps aux | grep bash

|| command1 || command2
Command2 is executed if, and only if, command1 returns a non-zero exit status i.e. command2 only runs if first command fails.
tar cvf user.tar.gz /home/user || mail -s ‘Backup failed’ user@domain.com < /dev/null && command1 && command2
Command2 is executed if, and only if, command1 returns an exit status of zero i.e. command2 only runs if first command1 run successfully.
apt-get update && apt-get upgrade

& command arg &
The shell executes the command in the background in a subshell. The shell does not wait until the command finish, and the return status is 0. The & operator runs the command in background while freeing up your terminal for other work. For example: find command is executed in background while freeing up your shell prompt.
find /home/user -name “*.jpg” > /tmp/usersjpg.txt &

; command1 ; command2
Separates commands that are executed in sequence. For example, ps is executed only after date command completes.
date ; ps