Service Management and Boot Troubleshooting

Question 1

How can the status of a service be viewed with ‘systemctl’?

Answer 1

■ systemctl status .

Question 2

How are ‘systemd’ loaded units listed by type?

Answer 2

■ systemctl {–type=unittype}

■ systemctl list-units {–type=unittype}

Question 3

How can loaded units for ‘systemd’ be listed?

Answer 3

■ systemctl {–type=unittype}

■ systemctl list-units

Question 4

How can installed units for ‘systemd’ be listed?

Answer 4

■ systemctl list-unit-files {–type=unittype}

Question 5

How can a service be prevented from starting?

Answer 5

■ By masking the configuration directories used in starting the service.
■ systemctl mask network - prevent network command usage

Question 6

What is the difference between a disabled service vs. a masked service?

Answer 6

■ A disabled service will not be started automatically at boot or by other unit files, but can be started manually. A masked service can not be started manually or automatically.

Question 7

What ‘systemd’ target supports multiple users, graphical and text-based logins?

Answer 7

■ graphical.target

■ systemctl isolate graphical.target

Question 8

What ‘systemd’ target supports multiple users, text-based logins only?

Answer 8

■ multi-user.target

■ systemctl isolate multi-user.target

Question 9

What ‘systemd’ target presents ‘sulogin’ prompt and basic system initialization?

Answer 9

■ rescue.target

■ systemctl isolate rescue.target

Question 10

What ‘systemd’ target presents ‘sulogin’ prompt, initramfs pivot complete and system root mounted on / read-only?

Answer 10

■ emergency.target

■ systemctl isolate emergency.target

Question 11

How is the default ‘systemd’ target set?

Answer 11

■ systemctl set-default {target}

Question 12

How is the default ‘systemd’ target listed?

Answer 12

■ systemctl get-default {target}

Question 13

What steps are required to change the boot time ‘systemd’ target?

Answer 13

1. Interrupt the boot loader menu countdown by pressing any key
2. Move the cursor to the entry to be started
3. Press ‘e’ to edit the current entry
4. Move to the line that starts with ‘linux16’
5. Append ‘systemd.unit={desired.target}’
6. Press Ctrl+x to boot with these changes.

Question 14

What line must be edited with the ‘systemd’ target and how?

Answer 14

■ The line that starts with ‘linux16’

■ ‘systemd.unit={desired.target}’ must be appended to the end

Question 15

How are the different available of ‘systemd’ listed?

Answer 15

■ systemctl -t help

Question 16

What steps are required to change a lost root password?

Answer 16

1. Interrupt the boot loader menu countdown by pressing any key
2. Move the cursor to the entry to be started
3. Press ‘e’ to edit the current entry
4. Move to the line that starts with ‘linux16’
5. Append ‘rd.break’
6. Remount the file system as read-write
   mount -oremount,rw /sysroot
7. Switch to chroot jail, where /sysroot is seen as root of the system tree
   chroot /sysroot
8. Change the root password
   passwd root
9. Set file system for relabeling
   touch /.autorelabel
10. Exit twice, the reboot

Question 17

How is ‘journald’ logging made persistent?

Answer 17

1. Make a directory to hold persistent logs
   ]# mkdir -p -m2775 /var/log/journal
2. Change group ownership to ‘systemd-journal’
   ]# chown :systemd-journal /var/log/journal
3. Tell ‘systemd-journald’ to reopen its logs
   ]# killall -USR1 systemd-journald

Question 18

How can logs from previous system boots be read?

Answer 18

■ journalctl -b-[number] -p [message level]
■ -b = boot logs
■ -[number] = boot ID
■ -p = message priority level
■ [message level] = (0)emerg,(1)alert,(2)crit,(3)err,(4)warning,(5)notice,(6)info,(7)debug
■ EX: journalctl -b-1 -p err

Question 19

What’s the difference between ‘emergency.target’ and ‘rescue.target’?

Answer 19

■ emergency.target keeps the root file system mounted read-only
■ rescue.target waits for ‘sysinit.target’ to complete first so that more of a system will be initialized

Question 20

How is the ‘early debug shell’ enabled?

Answer 20

■ systemctl enable debug-shell.service

■ Starts a root shell on TTY9 (Ctrl+Alt+F9). Root is automatically logged in; remember to disable it.

Question 21

What must be done after editing /etc/fstab?

Answer 21

■ Reload the systemd daemon

■ systemctl daemon-reload

Question 22

How is the emergency target used to fix boot problems?

Answer 22

1. Interrupt the boot loader menu countdown by pressing any key
2. Move the cursor to the entry to be started
3. Press ‘e’ to edit the current entry
4. Move to the line that starts with ‘linux16’
5. Append ‘emergency’
6. Press ‘Crtl+x’ to boot with these changes
7. Enter root password
8. Check if / file system is mounted read-only
9. Diagnose problem from here

Question 23

What grub2 file should not be edited manually by administrators? What tool is used to edit it?

Answer 23

■ /boot/grub2/grub.cfg

■ grub2-mkconfig

Question 24

Where can the grub menu timeout and other options be set before running grub2-mkconfig?

Answer 24

■ /etc/default/grub

Question 25

What command reinstalls the boot loader?

Answer 25

■ grub2-install