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Linux-Schnipsel

Nur simple Basics, keine Raketenwissenschaft.



Check which processes are using the most memory

with percentages:

ps aux --sort=-%mem | head -n 10

More specifically, with RSS (Resident Set Size in KB):
ps -eo pid,user,comm,%mem,rss --sort=-rss | head -n 10

with RSS in MB:
ps -eo pid,user,comm,%mem,rss --sort=-rss | \
awk 'NR==1 {print $0,"MB"} NR>1 {printf "%-8s %-10s %-20s %-6s %.2f MB\n",$1,$2,$3,$4,$5/1024}' | head -n 10

Top 10 processes using swap

smem -s swap -r | head -10

Without smem command:
for pid in /proc/[0-9]*; do
    swap=$(awk '/^Swap:/ {sum+=$2} END {print sum}' "$pid/smaps" 2>/dev/null)
    if [ "${swap:-0}" -gt 0 ]; then
        printf "%10d %10d KB %s\n" \
            "$(basename "$pid")" \
            "$swap" \
            "$(cat "$pid/comm" 2>/dev/null)"
    fi
done | sort -k2 -nr | head -10

ssh breaks find-loop in shellscript

#!/bin/bash

DIR=/testdir

find ${DIR} -maxdepth 1 -type f | while read FILE ; do
    # ohne </dev/null wird die Schleife nach dem ersten ssh beendet
    ssh servername "hostname;" </dev/null
done

Scan Network for a Service

nmap -p 22 --open -sV 192.168.0.0/24

Scans 192.168.0.1 - 192.168.0.254 for ssh-server (port 22)
You don't need root access for this

PID-File in bash-script

PID_FILE=/var/run/scriptname.pid

if [ -f $PID_FILE ]
then
    PID=$(cat $PID_FILE)
    ps -p $PID > /dev/null 2>&1
    if [ $? -eq 0 ]
    then
        echo "Process is already running!"
    exit 1
    else
        ## PID-File exists but process not running -> Update PID-File
        echo $$ > $PID_FILE
        if [ $? -ne 0 ]
        then
            echo "Error creating PID-file"
            exit 1
        fi
    fi
else
    echo $$ > $PID_FILE
    if [ $? -ne 0 ]
    then
        echo "Error creating PID-file"
        exit 1
    fi
fi

# ..... rest of the script

# at the end of the script, remove PID-File
rm $PID_FILE

Scrollen im Screen

- Press STRG-A
- Press ESC
- Scroll with UP and DOWN arrow keys
- Press ESC to Exit scrollback-mode

Kill process using grep

kill $(ps -ef | grep 'search' | grep -v grep | awk '{print $2}')
or
ps -ef |grep 'search' | grep -v grep | awk {'print $2'} | xargs kill
or
pkill -f search
-f The pattern is normally only matched against the process name. When -f is set, the full command line is used.

get external-ip

curl ifconfig.me

postfix - recipient address regex rewrite

rewrite localpart like google - remove +something from localpart

name+something@domain.tld will go to name@domain.tld

  • add file /etc/postfix/recipient_canonical with content:
    /^(.*)\+(.*)@eigeneMaildomain.ltd$/ ${1}@eigeneMaildomain.ltd
  • create the db file with postmap
    postmap /etc/postfix/recipient_canonical
  • add to /etc/postfix/main.cf
    recipient_canonical_maps = regexp:/etc/postfix/recipient_canonical
  • reload or restart postfix
    systemctl restart postfix

    crontab

    * * * * * <auszuführender Befehl>
    ┬ ┬ ┬ ┬ ┬
    │ │ │ │ │
    │ │ │ │ └──── Wochentag (0-7, Sonntag ist 0 oder 7)
    │ │ │ └────── Monat (1-12)
    │ │ └──────── Tag (1-31)
    │ └────────── Stunde (0-23)
    └──────────── Minute (0-59)

    Beim reboot bzw. nach dem booten ausführen:
    @reboot <auszuführender Befehl>

    Folgend Schreibweisen sind in der crontab auch möglich:
    @daily <auszuführender Befehl>
    @midnight <auszuführender Befehl>
    @hourly <auszuführender Befehl>
    @weekly <auszuführender Befehl>
    @monthly <auszuführender Befehl>
    @annually <auszuführender Befehl>
    @yearly <auszuführender Befehl>

    Alle Ausgaben nach /dev/null umleiten:
    * * * * * /pfad/script.sh > /dev/null 2>&1