lsof | grep '(deleted)'

sudo umount /dev/sdX1  # Размонтируем раздел
sudo extundelete /dev/sdX1 --restore-all

sudo apt install testdisk  # Устанавливаем пакет
sudo photorec

grep -a -b "текст из файла" /dev/sdX

systemd-analyze

systemd-analyze blame

systemctl disable сервис
systemctl mask сервис  # Полное отключение

systemctl disable gdm

tune2fs -o journal_async_commit /dev/sdX

tune2fs -c 0 /dev/sdX

nano /etc/default/grub

quiet splash systemd.legacy_boot=false

update-grub

apt install preload -y  # Для Debian/Ubuntu
yum install preload -y  # Для RHEL/CentOS

netstat -tulnp | grep :80

ss -tulnp | grep :80

lsof -i :80

# Debian/Ubuntu
apt install lsof  
# CentOS/RHEL
yum install lsof  

fuser -v 80/tcp

fuser -k 80/tcp

find / -type f -size +1G -exec ls -lh {} +

find /var/log -type f -size +500M -delete

du -ah / | sort -rh | head -20

top

htop

apt install htop  # для Debian/Ubuntu  
yum install htop  # для CentOS  
dnf install htop  # для Fedora  

mpstat -P ALL 1 5

apt install sysstat  # Debian/Ubuntu  
yum install sysstat  # RHEL/CentOS  

ps -eo pid,comm,%cpu --sort=-%cpu | head -n 10

ps -eo pid,ppid,user,%cpu,%mem,cmd --sort=-%cpu | head -n 6

ps -eo pid,ppid,user,%cpu,%mem,cmd --sort=-%mem | head -n 6

iotop -o -n 5

kill -9 PID

systemctl enable nginx

systemctl start nginx

systemctl status nginx

journalctl -u nginx --no-pager | tail -20

/usr/bin/python3 /opt/my_noscript.py &

chmod +x /etc/rc.local

crontab -e

@reboot /usr/bin/python3 /opt/my_noscript.py

lsof /путь/к/файлу

kill -9 PID

fuser -v /путь/к/файлу

fuser -k /путь/к/файлу

systemd-analyze

systemd-analyze blame

10.456s mysql.service  
5.321s docker.service  
3.214s networkd.service  

systemctl disable имя_сервиса --now

systemd-analyze critical-chain

systemd-analyze

sudo nano /etc/logrotate.conf

/var/log/*.log {
    daily
    rotate 7
    compress
    missingok
    notifempty
}

sudo truncate -s 0 /var/log/syslog
sudo truncate -s 0 /var/log/auth.log

sudo find /var/log -type f -name "*.log" -mtime +7 -delete

systemd-analyze

systemd-analyze blame

sudo systemctl disable <service>

sudo systemctl set-default multi-user.target

sudo nano /etc/default/grub

sudo update-grub

DefaultTimeoutStartSec=10s
DefaultTimeoutStopSec=10s

lsmod

blacklist модуль_название

sudo apt update && sudo apt install unattended-upgrades

sudo dpkg-reconfigure unattended-upgrades

sudo dnf install dnf-automatic -y

sudo systemctl enable --now dnf-automatic.timer

echo "0 3 * * * root apt update -y && apt upgrade -y" | sudo tee /etc/cron.d/autoupdate

dmesg | tail -50
journalctl -xe

mount | grep ro

mount -o remount,rw /

fsck -y /dev/sdX

smartctl -a /dev/sdX

apt install qemu-kvm libvirt-daemon-system virt-manager

egrep -c '(vmx|svm)' /proc/cpuinfo

virt-install --name testvm --ram 2048 --vcpus 2 --disk size=20 --os-variant ubuntu20.04 --cdrom /path/to/iso

virsh list --all
virsh start testvm
virsh shutdown testvm

top

htop

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

pidstat -r -p <PID> 5

pmap -x <PID>

valgrind --leak-check=full ./your_program

smem -t -k | head -20

[Service]
MemoryMax=500M

sudo nano /etc/ssh/sshd_config

#Port 22

Port 2222

sudo systemctl restart sshd

ssh -p 2222 user@server

PasswordAuthentication no

sudo systemctl restart sshd

sudo nano /etc/hosts.allow

sshd: 192.168.1.100

sshd: ALL

sudo apt install fail2ban -y

sudo nano /etc/fail2ban/jail.local

[sshd]
enabled = true
maxretry = 5
bantime = 3600

sudo systemctl restart fail2ban

sudo iptables -A INPUT -p tcp --syn --dport 2222 -m connlimit --connlimit-above 3 -j REJECT

find / -xtype l 2>/dev/null

find /home -xtype l

find / -xtype l -delete

rm /usr/bin/python
ln -s /usr/bin/python3 /usr/bin/python

find / -type l -exec ls -l {} +

ping -c 4 google.com

traceroute google.com

netstat -tulnp   # для старых систем
ss -tulnp        # альтернатива

dig google.com

tcpdump -i eth0 port 80

journalctl --disk-usage

Archived and active journals take up 2.3G in total.

journalctl --vacuum-size=500M

journalctl --vacuum-time=7d

[Journal]
SystemMaxUse=500M
SystemMaxFileSize=100M

systemctl restart systemd-journald