Red Hat System Administration I Flashcards (RH124)

1
$ whoami
2
mohammad

1
$ pwd
2
/home/mohammad

1
# Absolute
2
/home/mohammad/docs/file.txt
3
# Relative (from /home/mohammad)
4
docs/file.txt

1
$ man ls
2
$ man 5 passwd   # section 5 = file formats

1
$ whatis ls
2
ls (1) - list directory contents
3
$ ls --help

1
$ history
2
$ !42       # run command number 42
3
$ !!        # repeat last command

1
$ echo "Hello, World!"
2
$ echo $HOME
3
/home/mohammad

1
$ su -          # switch to root (full login shell)
2
$ sudo dnf update   # run one command as root

1
$ sudo -i
2
# whoami
3
root

1
$ ls -lah /etc

1
$ mkdir mydir
2
$ mkdir -p /tmp/a/b/c   # creates all parents

1
$ cp file.txt /tmp/
2
$ cp -r mydir/ /tmp/mydir_backup/

1
$ mv old.txt new.txt        # rename
2
$ mv file.txt /tmp/         # move

1
$ rm file.txt
2
$ rm -r mydir/
3
$ rmdir emptydir/

1
$ touch newfile.txt

1
$ ln file.txt hardlink.txt          # hard link
2
$ ln -s file.txt softlink.txt       # symbolic link

1
$ find /etc -name "*.conf"
2
$ find /home -type f -size +10M
3
$ locate passwd

1
$ cat /etc/hostname
2
$ less /var/log/messages
3
$ head -20 /etc/passwd
4
$ tail -f /var/log/secure

1
$ ls /etc > output.txt        # overwrite
2
$ echo "line" >> file.txt     # append
3
$ command 2>/dev/null         # discard errors

1
$ ps aux | grep httpd
2
$ cat /etc/passwd | wc -l
3
$ df -h | sort -k5 -rn

1
$ grep "root" /etc/passwd
2
$ grep -rn "error" /var/log/
3
$ grep -v "^#" /etc/ssh/sshd_config

1
$ wc -l /etc/passwd
2
45 /etc/passwd

1
# username:x:UID:GID:comment:home:shell
2
mohammad:x:1000:1000:Mohammad:/home/mohammad:/bin/bash

1
$ sudo useradd -m -s /bin/bash ali
2
$ sudo usermod -aG wheel ali    # add to wheel group
3
$ sudo userdel -r ali           # delete + home dir

1
$ sudo passwd ali       # set ali's password
2
$ passwd                # change your own password

1
$ sudo groupadd devteam
2
$ sudo usermod -aG devteam mohammad
3
$ sudo groupdel devteam

1
-rwxr-xr-- 1 root wheel 4096 Jan 1 12:00 script.sh
2
# owner: rwx, group: r-x, others: r--

1
$ chmod 755 script.sh        # rwxr-xr-x
2
$ chmod u+x,g-w file.txt     # symbolic
3
$ chmod -R 644 /var/www/html

1
$ sudo chown ali file.txt
2
$ sudo chown ali:devteam file.txt
3
$ sudo chown -R nginx:nginx /var/www/

1
$ umask          # view current umask
2
0022
3
$ umask 027      # set new umask

1
$ chmod u+s /usr/bin/someprog   # SUID
2
$ chmod g+s /shared/            # SGID on dir
3
$ chmod +t /tmp                 # sticky bit

1
$ ps aux
2
$ ps -ef
3
$ top
4
$ htop

1
$ kill 1234           # SIGTERM (default)
2
$ kill -9 1234        # SIGKILL
3
$ killall httpd
4
$ pkill -u ali        # kill all processes by user

1
$ sleep 300 &       # start in background
2
$ jobs              # list jobs
3
$ fg %1             # bring job 1 to foreground
4
$ bg %1             # resume job 1 in background

1
$ nice -n 10 tar czf backup.tar.gz /data
2
$ renice -n 5 -p 1234

1
$ pgrep sshd
2
$ pstree -p

1
$ ip addr show
2
$ ip addr show eth0
3
$ ip link show

1
$ ip route show
2
default via 192.168.1.1 dev eth0

1
$ nmcli connection show
2
$ nmcli device status
3
$ nmcli con up "Wired connection 1"

1
$ ping -c 4 8.8.8.8
2
$ traceroute google.com
3
$ ss -tuln         # listening ports

1
nameserver 8.8.8.8
2
nameserver 8.8.4.4
3
search example.com

1
$ ssh mohammad@192.168.1.10
2
$ ssh -p 2222 mohammad@server.example.com

1
$ ssh-keygen -t ed25519
2
$ ssh-copy-id mohammad@192.168.1.10

1
$ scp file.txt mohammad@server:/tmp/
2
$ rsync -avz /local/dir/ mohammad@server:/remote/dir/

1
Host myserver
2
  HostName 192.168.1.10
3
  User mohammad
4
  Port 2222
5
  IdentityFile ~/.ssh/id_ed25519

1
$ df -h
2
$ du -sh /var/log/
3
$ du -h --max-depth=1 /home/

1
$ lsblk
2
$ sudo fdisk -l /dev/sda
3
$ sudo blkid

1
$ sudo mkfs.xfs /dev/sdb1
2
$ sudo mkfs.ext4 /dev/sdb2

1
$ sudo mount /dev/sdb1 /mnt/data
2
$ sudo mount UUID="abc-123" /mnt/data
3
$ sudo umount /mnt/data

1
# device         mountpoint  fstype  options       dump pass
2
UUID=abc-123     /data       xfs     defaults      0    2

1
$ sudo pvcreate /dev/sdb
2
$ sudo vgcreate datavg /dev/sdb
3
$ sudo lvcreate -L 10G -n datalv datavg
4
$ sudo mkfs.xfs /dev/datavg/datalv

1
$ sudo lvextend -L +5G /dev/datavg/datalv
2
$ sudo xfs_growfs /data         # XFS
3
$ sudo resize2fs /dev/datavg/datalv  # ext4

1
$ sudo mkswap /dev/sdb2
2
$ sudo swapon /dev/sdb2
3
$ free -h
4
$ swapon --show

1
$ dnf repolist
2
$ sudo dnf config-manager --enable codeready-builder
3
$ ls /etc/yum.repos.d/

1
$ dnf module list
2
$ dnf module enable python39:3.9
3
$ dnf module install python39

1
$ dnf history
2
$ sudo dnf history undo 15

1
$ sudo systemctl enable --now sshd
2
# equivalent to enable + start in one command

1
$ systemctl get-default           # show default target
2
$ sudo systemctl set-default multi-user.target
3
$ sudo systemctl isolate rescue.target

1
$ systemctl --failed
2
$ systemctl status httpd.service

1
$ sudo mkdir -p /var/log/journal
2
$ sudo systemctl restart systemd-journald

1
$ echo $PATH
2
$ printenv HOME
3
$ export MYVAR="hello"   # set and export

1
$ MYVAR="local only"
2
$ export MYVAR           # now available to child processes
3
$ export MYVAR="hello"   # set and export in one step

1
#!/bin/bash
2
# My first script
3
echo "Hello, $USER!"
4
DATE=$(date +%Y-%m-%d)
5
echo "Today is $DATE"

1
#!/bin/bash
2
NAME="Mohammad"
3
UPTIME=$(uptime -p)
4
echo "Hello $NAME, uptime: $UPTIME"

1
#!/bin/bash
2
if [ -f /etc/passwd ]; then
3
  echo "File exists"
4
else
5
  echo "File not found"
6
fi

1
#!/bin/bash
2
for USER in ali sara omar; do
3
  echo "Creating user: $USER"
4
  sudo useradd $USER
5
done
6

7
for i in {1..5}; do
8
  echo "Number: $i"
9
done

1
#!/bin/bash
2
COUNT=1
3
while [ $COUNT -le 5 ]; do
4
  echo "Count: $COUNT"
5
  ((COUNT++))
6
done

1
#!/bin/bash
2
echo "Script: $0"
3
echo "First arg: $1"
4
echo "All args: $@"
5
echo "Count: $#"

1
$ ls /etc
2
$ echo $?    # 0 = success
3
$ ls /nonexistent
4
$ echo $?    # 2 = error

1
NAME="Mohammad"
2
echo '$NAME'   # prints: $NAME   (literal)
3
echo "$NAME"   # prints: Mohammad (expanded)

1
$ alias ll='ls -lah'
2
$ alias grep='grep --color=auto'
3
$ unalias ll