Linux System Administrator Technical Assessment

Explain the difference between a symbolic link and a hard link in Linux. When would you use each?

Answer explanation

A symbolic link points to a file by name and can link to directories, while a hard link points directly to the file's inode and cannot link to directories. Use symbolic links for flexibility and hard links for file system integrity.

What command would you use to find all files owned by user 'cifor' and larger than 100MB in the /var/log directory?

Answer explanation

Use the command 'find /var/log -user cifor -size +100M' to locate all files owned by user 'cifor' that are larger than 100MB in the /var/log directory. The '-user' option specifies the owner, and '-size +100M' filters by size.

Describe how to change the default run level in a systemd-based Linux distribution.

Answer explanation

To change the default run level in a systemd-based Linux distribution, edit the /etc/systemd/system/default.target file to point to the desired target (e.g., multi-user.target or graphical.target) and then reboot the system.

Write a command to find all processes using more than 10% of CPU and sort them by memory usage.

Answer explanation

Use the command 'ps aux --sort=-%mem | awk '$3>10'' to filter processes using more than 10% CPU and sort them by memory usage. The 'ps aux' lists processes, 'awk' filters based on CPU usage, and '--sort=-%mem' sorts by memory.

Explain the purpose of the following:

files/directories:

- /etc/fstab

- /proc

- /var/spool

- /etc/passwd

- /etc/shadow

Answer explanation

The files/directories serve specific purposes: /etc/fstab defines disk partitions, /proc contains process information, /var/spool holds queued data, /etc/passwd stores user account info, and /etc/shadow contains secure user passwords.

You notice that a Linux server is running out of disk space. Describe the steps you would take to identify which directories are consuming the most space and how you would address the issue.

Answer explanation

Use the 'du -h --max-depth=1' command to identify large directories. Then, use 'ncdu' for a more interactive view. Address space issues by deleting unnecessary files or moving data to another storage solution.

Describe your approach to patching critical vulnerabilities on Linux servers. Include considerations for testing, scheduling, and rollback procedures

Answer explanation

To patch critical vulnerabilities on Linux servers, I prioritize testing in a staging environment, schedule updates during off-peak hours, and implement rollback procedures using backups to ensure system stability.

What is the purpose of SELinux? How would you temporarily disable it for troubleshooting?

Answer explanation

SELinux (Security-Enhanced Linux) enforces security policies to protect the system. To temporarily disable it for troubleshooting, use the command 'setenforce 0'. This sets SELinux to permissive mode, allowing you to diagnose issues without enforcement.

Write the commands to:

- Check for pending security updates

- Apply only security updates

- Verify which packages were recently updated

Answer explanation

To check for pending security updates, use 'sudo apt list --upgradable'. To apply only security updates, use 'sudo apt upgrade --only-upgrade'. To verify recently updated packages, use 'grep " upgrade " /var/log/dpkg.log'.

Explain what a "privilege escalation vulnerability" is and list three common mitigation strategies.

Answer explanation

A privilege escalation vulnerability allows an attacker to gain elevated access to resources that are normally protected. Common mitigation strategies include regular software updates, implementing the principle of least privilege, and using security patches.