Linux Cheatsheet 03 — Process Management

ps aux                       # all processes, BSD style
ps -ef                       # all, full format
ps -eLf                      # threads too
ps aux | grep nginx
pgrep -fl nginx              # PID + cmdline
pgrep -u alice
pidof nginx

pstree
pstree -p                    # with PIDs
pstree -u                    # with users
pstree alice                 # for user

top
htop                         # interactive, better
btop                         # most modern

ps aux --sort=-%cpu | head
ps aux --sort=-%mem | head
ps -eo pid,user,pcpu,pmem,comm,args --sort=-pcpu | head

kill PID
kill -9 PID                  # SIGKILL (last resort)
kill -TERM PID               # graceful (default)
kill -HUP PID                # reload
killall nginx
pkill -f "python script"

TERM (15)  default; graceful
INT  (2)   ctrl-c
HUP  (1)   hangup; many daemons reload
QUIT (3)   ctrl-\; core dump
KILL (9)   unblockable
USR1, USR2 custom signals
STOP, CONT pause/resume

kill -l                      # list all

pkill -SIGTERM nginx
killall -USR1 nginx          # reopen logs

cmd &                        # background
jobs                         # list
fg %1                        # foreground
bg %1                        # background
ctrl-z                       # suspend
disown %1                    # remove from job table
nohup cmd &                  # outlive shell

nice -n 19 cmd               # low priority (1-19; 19 lowest)
nice -n -5 cmd               # high priority (requires root)
renice -n 10 -p PID

ionice -c 3 cmd              # idle I/O
ionice -c 2 -n 7 cmd         # best-effort low
ionice -c 1 -n 0 cmd         # realtime (root)

taskset -c 0,1 cmd           # pin to cores 0,1
taskset -p 0x3 PID           # bitmask

strace cmd
strace -p PID                # attach
strace -f -p PID             # follow forks
strace -e network cmd        # only network syscalls
strace -c cmd                # summary

ltrace cmd                   # library calls

lsof -p PID                  # open files
lsof -i                      # all sockets
lsof -i :80                  # what's on port 80
lsof /var/log/nginx.log      # who has this file open
lsof -u alice
lsof +D /var/log             # under dir

cat /proc/PID/cmdline
cat /proc/PID/status
cat /proc/PID/limits
cat /proc/PID/environ        # env vars (NUL separated)
ls -la /proc/PID/fd/         # open file descriptors
cat /proc/PID/io             # I/O stats

time cmd
# real    user    sys

at 14:00 << EOF
backup.sh
EOF

atq                          # list jobs

crontab -e
# m h dom mon dow command
0 2 * * * /opt/backup.sh

systemd-run --unit=temp --slice=user.slice -p MemoryMax=200M cmd

prlimit --as=536870912 cmd   # 512MB virtual memory limit
ulimit -v 524288             # 512MB (same)
ulimit -t 60                 # 60s CPU
ulimit -n 4096               # max open files
ulimit -u 100                # max processes

nohup cmd > out.log 2>&1 &
echo $!                      # PID

tmux new -s mywork
# inside: ctrl-b d to detach
tmux ls
tmux attach -t mywork

R running
S sleeping (interruptible)
D uninterruptible sleep (usually I/O wait)
Z zombie (finished, awaiting parent)
T stopped

ps -eo pid,state,comm | grep D

wait PID                     # in shell, wait for background