10 Unix Storage Interview Questions and Answers

Unix storage systems are fundamental to many enterprise environments, providing robust, scalable, and efficient solutions for data management. With their ability to handle large volumes of data and support for various file systems, Unix storage solutions are integral to maintaining the performance and reliability of critical applications. Mastery of Unix storage concepts is essential for professionals involved in system administration, data management, and IT infrastructure.

This article offers a curated selection of interview questions designed to test and enhance your understanding of Unix storage. By reviewing these questions and their detailed answers, you will be better prepared to demonstrate your expertise and problem-solving abilities in Unix storage during your next technical interview.

Unix Storage Interview Questions and Answers

1. Explain the concept of inodes and their role in Unix file systems.

In Unix file systems, an inode (index node) is a data structure that stores metadata about a file or directory, such as its size, ownership, permissions, and timestamps. Each file or directory is associated with an inode, which does not store the file name or the actual data content. The file name is stored separately in a directory entry, which points to the corresponding inode. This separation allows for efficient file operations, such as renaming or moving files, without altering the inode.

Key information stored in an inode includes:

• File type (e.g., regular file, directory, symbolic link)
• File size
• Owner and group IDs
• File permissions
• Timestamps (e.g., creation, modification, access times)
• Number of hard links
• Pointers to data blocks where the file’s content is stored

Inodes enable efficient file management by allowing quick lookups and modifications of file metadata without needing to traverse the entire file system.

2. Describe how to check disk usage.

To check disk usage in Unix, several commands can be utilized:

• df: Displays the amount of disk space available on the file system, including total space, used space, available space, and the mount point of each filesystem. For example, df -h shows disk usage in a human-readable format.
• du: Estimates file space usage for a specific directory or file. For example, du -sh /path/to/directory displays the total disk usage of the specified directory in a human-readable format.
• ls: With the -lh option, it displays the size of files in a directory in a human-readable format. While not specifically for disk usage, it can be useful for checking the size of individual files.

3. Write a script to find and delete files older than 30 days in a specific directory.

#!/bin/bash

# Directory to search
directory="/path/to/directory"

# Find and delete files older than 30 days
find "$directory" -type f -mtime +30 -exec rm -f {} \;

4. How would you create a symbolic link and what are its advantages over hard links?

To create a symbolic link in Unix, use the ln command with the -s option. A symbolic link, or symlink, is a file that points to another file or directory.

Example:

ln -s /path/to/original /path/to/symlink

Advantages of symbolic links over hard links:

• Cross-filesystem links: Symbolic links can span across different filesystems, whereas hard links cannot.
• Linking directories: Symbolic links can link to directories, while hard links are generally restricted to files.
• Independence from the original file: If the original file is deleted, the symbolic link remains, although it becomes a broken link. Hard links keep the data accessible as long as at least one link exists.
• Flexibility: Symbolic links can point to non-existent files, allowing for more flexible file management.

5. Explain the process of mounting and unmounting file systems.

Mounting a file system in Unix involves making it accessible at a certain point in the directory tree using the mount command. When you mount a file system, you attach it to an existing directory, known as a mount point.

Example command to mount a file system:

mount /dev/sda1 /mnt

Unmounting a file system detaches it from the directory tree using the umount command, ensuring all data is written to the disk and the file system is no longer accessible.

Example command to unmount a file system:

umount /mnt

6. Write a command to list all mounted file systems and their details.

To list all mounted file systems and their details in Unix, use the df command. This provides a summary of disk space usage for all mounted file systems.

Example:

df -h

The -h option makes the output easier to read by displaying sizes in a format that includes units (e.g., MB, GB).

The output includes columns such as:

• Filesystem: The name of the file system.
• Size: The total size of the file system.
• Used: The amount of space that is used.
• Avail: The amount of space that is available.
• Use%: The percentage of space that is used.
• Mounted on: The directory where the file system is mounted.

7. What is LVM and how does it benefit storage management?

LVM (Logical Volume Manager) is a device mapper framework that provides logical volume management for the Linux kernel. It allows administrators to create, resize, and manage disk storage more flexibly than traditional partitioning methods.

Benefits of LVM:

• Dynamic Resizing: LVM allows for resizing logical volumes without unmounting the filesystem.
• Snapshots: LVM supports creating snapshots, which are read-only copies of the filesystem at a specific point in time.
• Spanning Volumes: Logical volumes can span across multiple physical disks, allowing for larger storage volumes.
• Improved Disk Utilization: By pooling storage into volume groups, LVM can allocate space more efficiently.
• Ease of Management: LVM simplifies the management of disk storage, making it easier to add, remove, or resize storage as needed.

8. Describe the steps to extend a logical volume in LVM.

To extend a logical volume in LVM, follow these steps:

1. Identify the Volume Group (VG): Use the vgdisplay command to list all volume groups and their details.

2. Add Physical Volume (PV) to the Volume Group (VG): If needed, initialize a new disk or partition as a physical volume with pvcreate, and add it to the volume group using vgextend.

3. Extend the Logical Volume (LV): Use lvextend to extend the logical volume. You can specify the size to increase or use the -l +100%FREE option to use all available free space in the volume group.

4. Resize the Filesystem: After extending the logical volume, resize the filesystem to use the new space. Use resize2fs for ext4 filesystems or xfs_growfs for XFS filesystems.

Example commands:

# Display volume groups
vgdisplay

# Initialize a new disk as a physical volume
pvcreate /dev/sdx

# Add the new physical volume to the volume group
vgextend my_volume_group /dev/sdx

# Extend the logical volume
lvextend -l +100%FREE /dev/my_volume_group/my_logical_volume

# Resize the filesystem (ext4 example)
resize2fs /dev/my_volume_group/my_logical_volume

9. Write a script to monitor disk space and send an alert if usage exceeds 90%.

To monitor disk space and send an alert if usage exceeds 90%, use a shell script that utilizes common Unix commands such as df to check disk usage and mail to send an email alert. Below is an example script:

#!/bin/bash

THRESHOLD=90
EMAIL="[email protected]"

df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
do
  usage=$(echo $output | awk '{ print $1}' | sed 's/%//g')
  partition=$(echo $output | awk '{ print $2 }')
  if [ $usage -ge $THRESHOLD ]; then
    echo "Warning: Disk usage on $partition has reached $usage%" | mail -s "Disk Space Alert" $EMAIL
  fi
done

In this script:

• df -H is used to get the disk usage in human-readable format.
• grep -vE '^Filesystem|tmpfs|cdrom' filters out unnecessary lines.
• awk '{ print $5 " " $1 }' extracts the usage percentage and the partition name.
• The while read loop iterates over each line of output.
• The if statement checks if the usage exceeds the threshold and sends an email alert if it does.

10. Write a script to automate the backup of a directory to another server using rsync.

To automate the backup of a directory to another server using rsync, use a shell script. Rsync is a tool for synchronizing files and directories between two locations over a network. Below is an example script:

#!/bin/bash

# Variables
SOURCE_DIR="/path/to/source/directory"
DEST_USER="username"
DEST_HOST="remote.server.com"
DEST_DIR="/path/to/destination/directory"

# Rsync command
rsync -avz --delete $SOURCE_DIR $DEST_USER@$DEST_HOST:$DEST_DIR

# Logging
if [ $? -eq 0 ]; then
  echo "Backup completed successfully on $(date)" >> /var/log/backup.log
else
  echo "Backup failed on $(date)" >> /var/log/backup.log
fi

In this script:

• SOURCE_DIR is the path to the directory you want to back up.
• DEST_USER is the username on the remote server.
• DEST_HOST is the hostname or IP address of the remote server.
• DEST_DIR is the path to the destination directory on the remote server.
• The rsync command uses the -avz options for archive mode, verbose output, and compression, and the --delete option to remove files in the destination directory that are not present in the source directory.
• The script logs the success or failure of the backup operation to /var/log/backup.log.