Linux Interview questions beginner to expert ❤️

How do you check disk space usage in Linux?

df -h
du -sh * // To check size in particular directory only top lvl
du -ah . // Show size of file recursively

Where are system logs stored?

Most Linux logs are stored in /var/log/. Important logs include authentication logs, system logs, boot logs, and application logs.

/var/log/messages
/var/log/secure
/var/log/syslog
/var/log/boot.log

If a server is not starting properly, how do you debug it?

systemctl --failed
df -h
free -m
reboot logs

Explain file permissions and give execute permission.

Linux permissions are Read, Write, Execute for owner, group, others. To give execute permission to a user-owned file

chmod u+x script.sh     // For single user
chmod +x script.sh      // For all users
ls -l filename          // To view permission

How do you change file permissions?

chmod 755 file.sh
chmod +x file.sh

What does 777 permission mean?

777 means full permissions to owner, group, others.

7 = read + write + execute

• 4 = Read (r)

• 2 = Write (w)

• 1 = Execute (x)

Default permissions of file and directory?

Usually files get 644 and directories get 755 depending on umask.

Change ownership of file?

chown user:group file.txt

Root user but cannot create file?

I will check the disk space is full or not and check the i nodes once

df -h
df -i

Create user and assign group?

useradd rama
usermod -aG devops rama
userdel username

Create user in Linux?

useradd username  // To create user
passwd username   // To set Password
getent passwd     // To get list of users

Create Group in Linux ?

groupadd <groupname>        // To create a group
groupdel <groupname>       // to delete a group
getent group               // To get list of groups

Where are user details stored?

/etc/passwd → user info
/etc/shadow → encrypted passwords
/etc/group → groups

Disk free but cannot perform actions?

I will check disk space , i nodes and mount access whether it ro or rw

df -h
mount

Find largest files in directory?

du -ah . | sort -rh | head -10

What is zombie process?

A zombie process is completed child process whose parent has not collected exit status

ps -ef      // To get all process in full format 

Networking issue commands?

ping          //Checks basic network connectivity and latency             
nslookup      // Check DNS resolution
dig           // Advanced DNS lookup.
traceroute    // To trace route and hops
ip a          // Ip address
route -n

Server not coming after reboot?

If a server doesn’t come up after reboot, I first use console access to determine whether it’s a boot or network issue. Then I review boot logs with journalctl -xb, check failed services, disk space, /etc/fstab, network config, and SSH service. If needed, I boot into rescue mode for filesystem repair

Soft link vs Hard link?

Soft link

Shortcut to file/path

Breaks if original deleted

ln -s file link

Hard link
Same inode
Works even if original deleted

ln file link

What is journalctl used for ?

journalctl is used to check system logs, service logs, boot logs, kernel logs, and troubleshooting logs on Linux systems that use systemd