Objective 15 - LPI Linux Essentials Beta Exam

[015.1] What is the Linux superuser account called, and what UID does it have?

The superuser is root, and root has UID 0.

[015.1] What is the main difference between a standard user and root?

A standard user is unprivileged and operates within access-control limits; root has superuser-level control over the system.

[015.1] What are system accounts mainly used for?

They are typically used by operating-system facilities, programs, and services so those services do not need to run as root.

[015.1] What is root's home directory?

/root.

[015.1] In traditional shell prompts, what final character commonly indicates a normal user and what indicates root?

$ commonly indicates a non-privileged user shell; # commonly indicates a root shell.

[015.1] What does su do in the supplied LPI material?

It switches to another user; when no username is specified it commonly switches to root, using the target/root password.

[015.1] What does su - do when used to become root?

It starts a root login shell, using root's login environment.

[015.1] How does sudo differ from su in the supplied material?

sudo lets an authorized user run a command with elevated privileges and normally authenticates the current user with their own password; su switches user identity and commonly requires the target/root password.

[015.1] Why is sudo often preferable to sharing the root password?

Authorized users can elevate only as permitted without everyone needing to know the root password.

[015.1] [V2 explicit] What is ssh used for in objective 015.1?

Secure remote login to another system for shell access.

[015.1] [V2 explicit] What is scp used for in objective 015.1?

Securely transferring files using SSH.

[015.1] [V2 explicit] What is ssh-keygen associated with?

Generating SSH keys for public-key authentication.

[015.1] [V2 explicit] What authentication method does v2 explicitly require in addition to remote SSH login?

SSH public-key authentication.

[015.1] [V2 explicit] What is ~/.ssh/authorized_keys associated with?

It is the explicitly named SSH file used in public-key authentication to authorize login keys for a user account.

[015.1] Which v2 objective area combines sudo/su with ssh/scp?

015.1 Remote Logins, File Transfers and Elevated Permissions.

[015.1] Source-version gap: what major topic is new/explicit in v2 015.1 but was not part of the old v1.6 5.1 objective list?

Remote SSH login, secure file transfer, SSH key generation, and public-key authentication.

[015.2] What does UID mean?

User ID: the numeric identifier used to identify a user account.

[015.2] What does GID mean?

Group ID: the numeric identifier used to identify a group.

[015.2] What does id show?

User and group identity information such as UID, primary GID, and group memberships.

[015.2] What information is stored in /etc/passwd?

Basic local user-account information such as username, UID, primary GID, GECOS/comment, home directory, and login shell; the password hash is not stored there.

[015.2] What information is stored in /etc/shadow?

Local user password hashes and password-aging/expiration information; it is restricted compared with /etc/passwd.

[015.2] What information is stored in /etc/group?

Local group information such as group name, GID, and the listed group members.

[015.2] What is /etc/skel/ used for?

It is the skeleton directory whose files and directories can be copied into a newly created user's home directory.

[015.2] What does useradd do?

Creates a new user account.

[015.2] What does groupadd do?

Creates a new group.

[015.2] What is passwd primarily used for?

Changing a user's password; the supplied material also covers password status/aging controls.

[015.2] Can an ordinary user change their own password with passwd?

Yes. The supplied material states any user can change their own password, while root can change any user's password.

[015.2] What does w show?

Active logged-in users plus additional context such as uptime, load, and information about each active session.

[015.2] What does last show?

Previous login/session history; the supplied v1.6 material describes it as listing users who logged in last.

[015.2] [V2 explicit] What session-history term is newly listed alongside last in the v2 objective?

wtmpdb last.

[015.2] In a typical /etc/passwd entry, which fields identify the user numerically?

The UID field identifies the user; the primary GID field identifies the user's primary group numerically.

[015.2] What is the relationship between primary and additional groups?

Every user has a primary GID and may also belong to additional groups.

[015.3] In ls -l permissions, what three classes are shown after the file-type character?

Owner/user permissions, group permissions, and permissions for others.

[015.3] What do r, w, and x mean for a regular file?

r = read the file, w = modify/write the file, x = execute the file.

[015.3] What does r mean on a directory?

Permission to read/list the directory's entries.

[015.3] What does w mean on a directory?

Permission related to creating, deleting, or renaming entries in the directory, subject to the other required permissions.

[015.3] What does x mean on a directory?

Permission to enter/traverse the directory and access entries by name when other permissions allow it.

[015.3] What numeric values correspond to r, w, and x?

r = 4, w = 2, x = 1.

[015.3] Convert chmod 755 to symbolic permissions.

rwxr-xr-x: owner = rwx, group = r-x, others = r-x.

[015.3] Convert chmod 640 to symbolic permissions.

rw-r-----: owner = rw-, group = r--, others = ---.

[015.3] Convert rw-rw---- to numeric permissions.

660.

[015.3] In symbolic chmod notation, what do u, g, o, and a mean?

u = user/owner, g = group, o = others, a = all three classes.

[015.3] In symbolic chmod notation, what do +, -, and = mean?

• adds permissions, - removes permissions, and = sets the specified permissions exactly for the selected class.

[015.3] Interpret: chmod g+w file.txt

Add write permission for the file's owning group without intentionally changing the other permission bits.

[015.3] Interpret: chmod u+x,go-wx script.sh

Add execute for the owner, and remove write and execute permissions from group and others.

[015.3] What does chown change?

The ownership of a file or directory; the supplied material shows syntax that can change the owning user and/or group.

[015.3] Interpret: chown carol:students text.txt

Set carol as the owning user and students as the owning group of text.txt.

[015.3] If the current user owns a file, which permission class is applied to that user according to the supplied material?

The owner/user permission bits are applied; the system does not fall through to more-permissive group or others bits for that same user.

[015.4] What is /tmp used for, and should programs assume its files survive indefinitely?

/tmp is for temporary files; programs should not assume files there will be preserved between invocations, and systems commonly clear it at boot although this is not mandatory.

[015.4] How does /var/tmp differ from /tmp in the supplied material?

/var/tmp is also for temporary files, but files there should normally persist across system reboots.

[015.4] What does the sticky bit do on a shared writable directory?

It prevents users from removing or renaming files in that directory unless they own the file or the directory.

[015.4] How is the sticky bit commonly shown in ls -l output for a directory such as /tmp?

As t in the others-execute position, for example drwxrwxrwt.

[015.4] How can you add the sticky bit symbolically to a directory?

chmod +t DIRECTORY.

[015.4] What does ln -s TARGET LINK_NAME create?

A symbolic (soft) link named LINK_NAME that points to the path TARGET.

[015.4] What happens to a symbolic link if its target is deleted?

The symbolic link itself still exists, but it becomes broken because its target path no longer resolves.

[015.4] How can you recognize a symbolic link in ls -l output?

The file type begins with l, and the listing commonly shows LINK_NAME -> TARGET.