Table of Content
Weight: 4
Description: Candidates should be able to perform basic process management.
Key Knowledge Areas:
- Run jobs in the foreground and background
- Signal a program to continue running after logout
- Monitor active processes
- Select and sort processes for display
- Send signals to processes
Terms and Utilities:
& bg fg jobs kill nohup ps top free uptime pgrep pkill killall screen
&
run in background
bg, fg, jobs
nohup
running process after logout
- ignore hangup signal and append stdout and stderr to file
- cannot run pipeline or command list, only for script
echo "while sleep 30; do date; done" > test.sh nohup bash test.sh &
nohup bash -c ‘killall wvdial ; sleep 60; wvdial’
ps
ps $(jobs -p) -f full -j jobs -l long --forest process tree -C command -u user --sort -sid,+comm ps -j --forest ps -ef ps -fl ps -C getty -o user, pid, tty, time, comm
top
top -o %MEM
free
memory usage
free -mt # totally line in mb
uptime
load average for last 1,5,15 mins
oldhorse@dclab-u1504s:~$ free -mt
total used free shared buffers cached
Mem: 480 275 205 4 49 120
-/+ buffers/cache: 105 375
Swap: 2044 0 2044
Total: 2525 275 2250
kill
oldhorse@dclab-u1504s:~$ kill -l 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 Signal Meaning Usage SIGTERM Terminate now (unless you can handle a SIGTERM) kill pid kill -TERM pid kill -15 pid SIGHUP The modem hung up (or reload your configuration file if you’re not a terminal application) kill -HUP pid kill 1 pid SIGINT A user pressed Ctrl+C – interrupt and exit Ctrl+C SIGSTOP A user pressed Ctrl+Z – suspend Ctrl+Z kill -STOPpid SIGCONT Continue fg or bg kill -CONT pid kill -s SIGTSTP %1 jobs -l kill -s SIGCONTkill -s SIGTERM %2 killall -HUP inetd # reload after inetd.conf change
pgrep , pkill, killall
pgrep -a process pkill -e process # echo which process killed root@dclab-u1504s:~# pgrep -a sudo 1980 sudo nohup . test.sh root@dclab-u1504s:~# killall -i sudo Kill sudo(1980) ? (y/N) y
screen
1st term screen -S sockname -L # turn on logging, check screenlog.x under current folder 2nd term screen -ls screen -r screenname # attach to detached screen screen -x screenname # attach to not detached screen
Quiz questions
1. What is a background process? 2. Name 4 ways you can kill a process which is in your jobs list. 3. How can you use ps to show a tree of processes similar to pstree? 4. What is the default signal sent by kill and killall? 5. If you have a process's name but not it's PID, what can you do to send a signal to it? 6. What will each of the following commands do, and who may run them? killall -HUP init kill -1 1 7. What happens if you kill 9 a process which is doing interactive console handling like man or vi?
Answers to quiz questions
1. A process which is not receiving terminal keyboard input. 2. kill %1; fg and Ctrl+C; killall processname; kill 9112 (giving PID of process) 3. ps -axf 4. SIGTERM (terminate, signal 15) 5. Use killall rather than kill 6. Both send a hangup to process 1, init. This causes init to reload its configuration file /etc/inittab. 7. The console may be in an undefined state, and may have to be reset with the command reset or stty sane.