q23-process-management

Énoncé§

Solve this question on: app-srv1

1. Find the PID of the process listening on TCP port 8080 and write it into /opt/course/23/pid.
2. Renice the process stress-ng to priority 10 without killing it.
3. Send SIGTERM to all sleep processes owned by user bob.
4. Identify the top 3 memory-consuming processes and write their command names into /opt/course/23/top-mem.

Solution§

Step 1 — Find the process behind a port§

sudo ss -tlnp | grep :8080
# LISTEN 0 511 *:8080 *:* users:(("node",pid=1423,fd=18))
sudo ss -tlnp 'sport = :8080'
sudo lsof -i :8080
sudo fuser 8080/tcp

Pull just the PID:

sudo ss -tlnpH 'sport = :8080' | grep -oP 'pid=\K[0-9]+' > /opt/course/23/pid

Step 2 — Change priority§

Nice values range from -20 (highest priority) to 19 (lowest). Only root can lower (more negative) the niceness.

ps -eo pid,ni,cmd | grep stress-ng
sudo renice -n 10 -p $(pgrep stress-ng)
# or rename whole process group / user
sudo renice -n 10 -u bob
sudo renice -n 10 -g 1234

Start a process with a given priority:

nice -n 15 ./long-job.sh
chrt -f 50 ./realtime-job                  # real-time scheduling
ionice -c 3 ./bulk-copy.sh                 # I/O idle class

Step 3 — Kill processes selectively§

pgrep -u bob sleep                          # list matching PIDs
sudo pkill -SIGTERM -u bob sleep            # signal them
sudo killall -u bob sleep                   # by name

Signals worth knowing:

• SIGHUP (1) — reload config (many daemons)
• SIGINT (2) — Ctrl+C
• SIGKILL (9) — uncatchable, immediate
• SIGTERM (15) — polite termination, default
• SIGSTOP / SIGCONT — pause / resume

Step 4 — Top memory consumers§

ps -eo pid,comm,%mem --sort=-%mem | head -n 4
ps -eo pid,comm,%mem --sort=-%mem | awk 'NR>1 && NR<=4 {print $2}' > /opt/course/23/top-mem

Live monitoring§

top                # interactive — press M (mem), P (cpu), k (kill)
htop               # nicer alternative
pidstat 1          # per-process CPU/mem every second
vmstat 1           # global counters
iotop              # I/O per process (needs root)

Background and job control§

./long.sh &                       # background
jobs                              # list shell jobs
fg %1                             # foreground job 1
bg %1
nohup ./long.sh &                 # survive shell logout
disown %1                         # detach existing job