Permissions, processes, filesystems, packages and logs — worked through as ten short quizzes. These are the questions that come up in a screening round for any backend, SRE, DevOps or support role, and the ones that get skipped because nobody sits down and revises them.

Linux Fundamentals

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/var/spool for the data it can regenerate, and /var/tmp for the state it must keep

/var/lib for the data it can regenerate, and /var/spool for the state it must keep

/var/tmp for the data it can regenerate, and /var/cache for the state it must keep

/var/cache for the data it can regenerate, and /var/lib for the state it must keep

A packaging review asks where an application should write two kinds of data: one it can regenerate from an upstream source and can safely lose, and one it must keep across reboots or it stops working.

Which pair of directories does the Filesystem Hierarchy Standard intend?

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Linux Fundamentals — Filesystem Layout and Navigation (Practice Quiz)

notes.txt, because deleting it would invalidate copy.txt, which is what proves it to be the original

notes.txt, because the inode stores the name the file was created with and treats later names as aliases of it

copy.txt, because the most recently created entry becomes the primary name and the earlier one is demoted to a link

Neither — both are directory entries of equal standing referring to the same inode, and nothing records which was created first

You create a file notes.txt, then run `ln notes.txt copy.txt`. A colleague asks which of the two names is the original.

What is the accurate answer?

Linux Fundamentals — Files, Links and Inodes (Practice Quiz)

The account has no password set and can be logged into without one

The password hash is not stored here; it lives in /etc/shadow, which unlike this file is not world-readable

The password is stored here but obscured, and the x is the first character of the obscured form

The account is disabled and cannot be used for login by any means

A line in /etc/passwd reads:

    deploy:x:1004:1004:Deploy account:/home/deploy:/bin/bash

What does the x in the second field mean?

Linux Fundamentals — Users, Groups and sudo (Practice Quiz)

dpkg installs for the current user only, while apt installs system-wide and therefore has access to the shared dependency database

dpkg acts only on the file it is given and reports missing dependencies as an error; apt reads repository metadata and fetches them

dpkg verifies dependencies more strictly, while apt installs the package regardless and leaves the dependencies unresolved

dpkg can only install packages that came from a configured repository, while apt can install from any local file

On a Debian-family system, `dpkg -i app.deb` fails with unmet dependencies, while `apt install ./app.deb` on the same file succeeds.

What is the difference between the two tools?

Linux Fundamentals — Package Management (Practice Quiz)

The default is SIGTERM, which the kernel delivers only when the process is idle; SIGKILL is delivered immediately regardless of state

Both are the same signal, and the difference is that specifying it numerically bypasses the shell's confirmation prompt

The default is SIGTERM, which a program may catch and handle so it can shut down cleanly; SIGKILL can be neither caught nor ignored and is acted on by the kernel

The default is SIGKILL and signal 9 is SIGTERM, so the second attempt succeeded because it gave the process a chance to exit

A process ignores the default signal sent by kill, so an administrator sends signal 9 instead and it dies immediately.

What is the difference between the two signals?

Linux Fundamentals — Processes, Signals and Jobs (Practice Quiz)

The service started but crashed during the boot sequence, and enable would have configured it to be retried

start runs the service in the foreground and it exits when the session that started it ends, including at shutdown

The unit needed a daemon-reload after starting, without which the change is not written to persistent state

start affects the running system only; enable is what arranges for the unit to be started at boot

You run `systemctl start nginx` and the service comes up. After a reboot it is not running.

What was missed?

Linux Fundamentals — systemd and Services (Practice Quiz)

The value was rejected as it contains digits, and variables passed to children must be alphabetic

Scripts are given a cleared environment by default, so no variable set in the parent shell is ever visible to them

Without export the assignment creates a shell variable that is not part of the environment, and only the environment is passed to a child process

The script runs before the assignment is committed, because assignments take effect only at the next prompt

You set `TOKEN=abc123` at a shell prompt, then run a script that reads TOKEN. The script sees nothing.

Why?

Linux Fundamentals — Environment Variables and Startup Files (Practice Quiz)

Neither list it nor enter it, because she falls in the other class and that field grants nothing

Enter it but not list it, because the leading d grants traversal to every user regardless of the fields

Both, because the group field applies to any user who is not the owner, and it grants read and execute

List it but not enter it, because the read bit is the one the other class always retains on a directory

`ls -l` shows `drwxr-x--- 2 alice devs 4096 Mar 3 10:12 reports`, and no ACLs are set on it. carol is an unprivileged user who is not alice and is not a member of devs.

What can carol do with reports?

Linux Fundamentals — Permissions, Ownership and umask (Practice Quiz)

Available space is reported per user according to quota, and the superuser has no quota configured

The superuser's writes are buffered in memory and only flushed once space becomes available

A percentage of blocks is reserved for the superuser at filesystem creation, which keeps a full disk from stopping privileged processes from recovering it

The superuser writes bypass the filesystem's allocator and go directly to the underlying block device

An ext4 filesystem created with mke2fs defaults reports 0 bytes available to an ordinary user, but the superuser can still write to it.

What explains that?

Linux Fundamentals — Disks, Mounts and Space (Practice Quiz)

Messages from the first boot recorded in the journal, counting forward from the oldest

Messages from the previous boot, which is how you investigate a crash after the machine has come back up

The last message from the current boot, with -1 limiting the number of lines

Messages from the last hour, with -1 interpreted as a relative time offset

journald is configured with `Storage=persistent`, and the machine has been rebooted at least once.

What does `journalctl -b -1` show?

Linux Fundamentals

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