Temp Files

Question 1

Which service manages the lifecyle of temp files

Answer 1

systemd-tempfiles-setup

Question 2

What does systemd-tmpfiles-setup service do?

Answer 2

create, delete, and clean up volatile and temporary files and directories.

Question 3

where is the config that systemd uses to manage systemd-tmpfiles-setup service located?

Answer 3

/usr/lib/systemd/system/systemd-tmpfiles-setup.service

Question 4

Diff between:

/usr/lib/systemd/system/systemd-tmfiles-setup.services

and files in

/usr/lib/tmpfiles.d/,
      /run/tmpfiles.d/,
      /etc/tmpfiles.d/

Answer 4

First is a config file for systemd telling it how to start and manage systemd-tmpfiles-setup

The second set of files are config files for systemd-tmpfiles-setup.

Question 5

What are location of config files for systemd-tmpfiles-setup:

Answer 5

1) /usr/lib/tmpfiles.d/
2) /run/tmpfiles.d/
3) /etc/tmpfiles.d/

Question 6

In what order are systemd-tmpfiles.setup config files evaluated?

Answer 6

1) /usr/lib/tmpfiles.d/.conf
2) /run/tmpfiles.d/.conf
3) /etc/tmpfiles.d/*.conf

Question 7

Explain tmp file cleanup process

Answer 7

timer unit

systemd-tmpfiles-clean.timer

periodically call

systemd-tmpfiles-clean.service

to do the cleaup as per configurations in:

1) /usr/lib/tmpfiles.d/
2) /etc/tmpfiles.d/
3) /run/tmpfiles.d/

Question 8

What are the different systemd unit types?

Answer 8

1) Service Units
2) Socket Units
3) Device Units
4) Mount Units
5) Automount Units
6) Target Units (.target):
7) Timer Units (.timer):
8) Path Units (.path):
9) Slice Units (.slice):
10) Scope Units (.scope):

Question 9

Explain:

q /tmp 1777 root root 10d

Answer 9

tmpfile config of /usr/lib/tmfiles.d/tmp.conf

says that files under /tmp will be purged after 10d if not accessed.

Question 10

How do you modify the content of

/usr/lib/tmfiles.d/tmp.conf

Answer 10

1) Copy it to following location and modify the copy. Then run the clean command.

/etc/tmfiles.d/tmp.conf

systemd-tmpfiles --clean  etc/tmfiles.d/tmp.conf

Question 11

Create a new folder and define its cleanup policy

Answer 11

echo 'q /home/student/momentary 0700 root root 30s' > /etc/tmpfiles.d/momentary.conf

systemd-tmpfiles --create /etc/tmp files.d/momentary.conf

Question 12

What is special about the /run folder

Answer 12

exists only in memory

Question 13

What command does systemd-tmpfiles-setup calls to do its job?

Answer 13

systemd-tmpfiles

Question 14

Show the content of a timer unit

Answer 14

systemctl cat systemd-tmpfiles-clean.timer

Question 15

How does a timer know when to invoke the service it is meant to invoke?

Answer 15

In the config file of the timer, there is a [Timer] section for this purpose

Question 16

What fields are used to control when the timer will invoke the service it is supposed to control?

Answer 16

1) OnBootSec=15min
2) OnUnitActiveSec=1d

Question 17

Explain the command:

d /run/systemd/seats 0755 root root -

Answer 17

1) create dir /run/systemd/seats
2) chown root:root
3) chmod 0755
4) If directory exists, do nothing.
5) systemd-tmpfiles does not purge this directory.

Question 18

Explain the command:

D /home/student 0700 student student 1d

Answer 18

1) create dir /home/student directory
2) chown student:student
3) chmod 0700
4) If directory exists, wipe its content.
5) systemd-tmpfiles purges this directory after 1d inactivity.

Question 19

Explain the command:

L /run/fstablink - root root - /etc/fstab

Answer 19

1) create link /run/fstablink pointing to /etc/fstab
2) chown root:root
3) systemd-tmpfiles never purges this link

Question 20

OnBootSec=15min

Answer 20

Interval between system boot and first service activation

Question 21

OnUnitActiveSec=1d

Answer 21

Interval between successive timer activations

Question 22

Similarity between systemd-tmpfiles-setup and systemd-tmpfiles-clean services

Answer 22

They all use systemd-tmpfiles command to create, delete, purge.

Question 23

Diff between systemd-tmpfiles-setup and systemd-tmpfiles-clean services

Answer 23

Setup runs at boot time, clean runs according to timer.