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How to Use the diff Command in Linux

How to Use the diff Command in Linux
Awais Khan
Technical writer
Linux
17.10.2024
Reading time: 7 min
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The diff command in Linux is a powerful tool that allows users to compare files and directories. With the help of this command, one can identify differences between files, and perform tasks like code reviews, configuration management, and version control. 

This tutorial will guide users through what is the diff command, its possible methods, and practical examples.

Introduction

The diff command is used in Linux to compare the content of two files line by line. When executed, this command analyzes the two files and outputs the differences in a specific format. The output shows which lines need to be added, deleted, or changed to make the files identical.

Basic Syntax and Options for diff

The basic syntax for the Linux diff command is provided below:

diff [options] file1 file2

Here,

  • diff is the command itself.

  • [options] are optional flags used to modify the behavior of the diff Linux command.

  • file1 and file2 are the two files used for Linux file comparison.

The following table describes a few options that can be used with diff:

Option

Description

-a

Process every file as a text file and perform a line-by-line comparison.

-b

Does not consider white space differences.

-c

Show differences with a few lines of context around them.

-d

Opt for a different algorithm to pinpoint a more concise set of changes.

-e

Output an ed script.

-E

Ignore changes due to tab expansion.

--binary

Compare files in binary mode.

-i

Ignore case differences in file contents.

-l

Paginate the output through pr.

-N

Treat absent files as empty.

-q

Report only when files differ.

-s

Report when files are identical.

-u

Display output in a unified format, showing differences more compactly.

-w

Ignore all white space.

For more details and to explore more options, the users can get help by opening the diff manual using the following command:

man diff

Comparing Two Text Files Using diff

There are two ways to compare files on Linux with diff.

Basic Comparison of Two Text Files

The basic way to use the diff in Linux is to compare two files line by line and display their differences. To compare two text files, file1.txt and file2.txt, one can use the following command:

diff file1.txt file2.txt

This command will output the differences between file1.txt and file2.txt.

Image1

Display Differences in a Unified Format

For a more readable format, the -u option can be used with diff. This option provides a unified format that includes a few lines of context around the differences. This makes it easier to understand the changes. Follow the command provided below:

diff -u file1.txt file2.txt

Image3

The unified format output includes line numbers, context lines, and change indicators. Lines starting with - indicate deletions, lines starting with + indicate additions and lines starting with a space are unchanged context lines.

Using diff for Directory Comparisons

The Linux command diff can also be used to compare directories, it can be done using the -r option. For example:

diff -r dir1 dir2

The above command when executed will recursively compare all files and subdirectories within dir1 and dir2.

Image2

Understanding diff Output and Symbols

The diff output uses specific symbols to indicate changes, these are provided below:

  • ---: Denotes the first file.

  • +++: Denotes the second file.

  •  @@ -1,4 +1,4 @@: This line is part of the unified diff format. It gives context about where the changes are happening in the files. @@ indicates the start of a change hunk. -1,4 means the chunk starts at line 1 in the first file and spans 4 lines. +1,4 means the chunk starts at line 1 in the second file and spans 4 lines.

  • <: This marker signifies lines that exist in the first file but not in the second one. Such lines must be removed from the first file to match the second file exactly.

  • >: This marker indicates lines that are in the second file but not in the first one. These lines should be added to the first file to make it identical to the second file.

  • -: This marker shows lines that have been deleted from the first file.

  • +: This marker indicates lines that have been inserted into the second file.

Let’s look at an example to make it clearer.

Suppose there are two files, file1.txt and file2.txt.

Contents of file1.txt:

apple
banana
cherry
date

Contents of file2.txt:

apple
banana
date
raspberry

Running the command diff file1.txt file2.txt will produce the following output:

Image1

Here’s how to interpret this output:

  • 3d2: This means that line 3 in file1.txt (cherry) needs to be deleted to match file2.txt. The d stands for "delete".

  • < cherry: This indicates that cherry is present in file1.txt but not in file2.txt.

  • 4a4: This means that after line 4 in file1.txt, users need to add "raspberry" to match file2.txt. The a stands for "add".

  • > raspberry: This indicates that raspberry is present in file2.txt but not in file1.txt.

Creating Patch Files with diff

To create a patch file, the -u (unified) option is used, which provides a more readable format by showing a few lines of context around the changes. The output is then redirected to a file, typically with a .patch extension. For example:

diff -u file1.txt file2.txt > changes.patch

  • diff -u: Compares file1.txt and file2.txt and generates a unified diff.

  • >: Redirects the output to a file named changes.patch.

Image4

To apply the patch, use the patch command like this:

patch file1.txt < changes.patch

Image7

Using diff with Various Output Formats

The diff also supports multiple output formats, here are a few examples.

Unified Format

This format gives users a snapshot of the changes with a few lines of context before and after each change. It’s great for quickly seeing what was added or removed.

diff -u file1.txt file2.txt

Image6

Context Format

This format shows more surrounding lines for each change and gives users a bigger picture of where the changes happened.

diff -c file1.txt file2.txt

Image9

Side-by-Side Format

This format places the two files next to each other and makes it easy to compare them line by line.

diff -y file1.txt file2.txt

Image8

Brief Format

This format gives a summary of whether the files differ but does not show the actual changes.

diff -q file1.txt file2.txt

Image11

Practical Examples of Using diff

Here are some practical examples of using the diff command in Linux.

Ignoring Case Differences

When comparing files, sometimes the case of the letters might differ, but the content is essentially the same. The -i option is used to ignore case differences. For example: 

diff -i file3.txt file4.txt

In this example, diff will treat "Hello" and "hello" as identical, ignoring the case difference.

Image10

Ignoring White Space

White space differences, such as extra spaces or tabs, can be ignored using the -w option. This is useful when formatting changes have been made but the content remains the same. For example:

diff -w file1.txt file2.txt

Here, diff will ignore all white spaces, treating "Hello   World" and "Hello World" as identical.

Comparing Binary Files

The diff in Linux can also be used to compare binary files using the --binary option. This is helpful when users need to check if two binary files are identical or not. For example:

diff --binary file1.bin file2.bin

In this case, diff will compare the binary data of file1.bin and file2.bin and report any differences.

Ignoring Blank Lines

To ignore blank lines when comparing files, simply use the -B option, which is useful when blank lines have been added or removed.

diff -B file1.txt file2.txt

Conclusion

The diff is a versatile command in Linux for comparing files and directories. By understanding its syntax, options, and output formats, users can efficiently identify differences and manage changes. Whether for code reviews, configuration management, or version control, the diff command is an essential part of any Linux user’s toolkit.

On Hostman, you can try Linux VPS hosting for your projects. 

Linux
17.10.2024
Reading time: 7 min
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How to Use Telnet Command on Linux

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24 July 2025 · 6 min to read
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How to Set Up Backup with Bacula

Bacula is a cross-platform client-server open source backup software that enables you to back up files, directories, databases, mail server data (Postfix, Exim, Sendmail, Dovecot), system images, and entire operating systems. In this guide, we’ll walk you through the process of installing and configuring Bacula on Linux, as well as creating backups and restoring user data. To get started with Bacula, you’ll need a server or virtual machine running any Linux distribution. In this tutorial, we’ll be using a cloud server from Hostman with Debian 12. Bacula Architecture Bacula’s architecture consists of the following components: Director (Bacula Director) The core component responsible for managing all backup, restore, and verification operations. The Director schedules jobs, sends commands to other components, and writes information to the database. Storage Daemon (Bacula Storage) Handles communication with storage devices such as disks, cloud storage, etc. The Storage Daemon receives data from the File Daemon and writes it to the configured storage medium. File Daemon (Bacula File) The agent installed on client machines to perform the actual backup operations. Catalog A database (MySQL, PostgreSQL, or SQLite) used by Bacula to store information about completed jobs, such as backup metadata, file lists, and restore history. Console (Bacula Console, bconsole) A command-line utility for interacting with Bacula. The Console allows administrators to control the Director via a CLI. GUI tools such as Bacula Web and Baculum are also available. Monitor (Optional) A component for monitoring the Bacula system status. It tracks job statuses, daemon states, and storage device conditions. Creating Test Data for Backup Let’s create some test files to use in our backup. Create a test directory and navigate into it: mkdir /root/test_backups && cd /root/test_backups Now create six sequential files: touch file{1..6}.txt Also, create a directory in advance for storing restored files: mkdir /root/restored-files Installing Bacula In this tutorial, we will install all Bacula components on a single server. However, Bacula also supports a distributed setup where components such as the Director, Storage Daemon, Client, and database can be installed on separate servers. This decentralized setup is suitable for backing up multiple systems without overloading a single server. We'll be using Debian 12 and installing PostgreSQL (version 15) as the backend database. Update the package index and install Bacula (server and client components): apt update && apt -y install bacula-server bacula-client PostgreSQL 15 will also be installed during this process. During installation: When prompted with: “Configure database for bacula-director-pgsql with dbconfig-common?”, press ENTER. When asked to choose the database host, select localhost, since we are installing everything on one server. When prompted with: “PostgreSQL application password for bacula-director-pgsql”, set a password for the Bacula database.  Do not leave this field empty, or a random password will be generated. Re-enter the password when asked to confirm. The installation will then continue normally. After the installation is complete, verify the status of Bacula components and PostgreSQL. Check the status of the Bacula Director: systemctl status bacula-director Check the Storage Daemon: systemctl status bacula-sd Check the File Daemon: systemctl status bacula-fd Check PostgreSQL: systemctl status postgresql If all components display a status of active, then Bacula has been successfully installed and is running. Bacula Configuration Bacula is configured by editing the configuration files of the program components. By default, all Bacula configuration files are located in the /etc/bacula directory. Next, we will configure each Bacula component individually. Configuring Bacula Director Using any text editor, open the bacula-dir.conf configuration file for editing: nano /etc/bacula/bacula-dir.conf Let’s start with the Director block, which sets the main configuration parameters for the Director component: Director { Name = 4142939-bi08079-dir DIRport = 9101 QueryFile = "/etc/bacula/scripts/query.sql" WorkingDirectory = "/var/lib/bacula" PidDirectory = "/run/bacula" Maximum Concurrent Jobs = 20 Password = "ohzb29XNWSFISd6qN6fG2urERzxOl9w68" Messages = Daemon DirAddress = 127.0.0.1 } Explanation of parameters: Name: The name of the Director component. This is a unique identifier used to connect with other components like the File Daemon and Storage Daemon. By default, it includes the server's hostname and the -dir suffix. Example: 4142939-bi08079-dir. DIRport: The port that Bacula Director listens to for incoming connections from the management console (bconsole). Default is 9101. QueryFile: Path to the SQL script file used to run queries on the database. It contains predefined SQL queries for job management, verification, data restoration, etc. Default: /etc/bacula/scripts/query.sql. WorkingDirectory: The working directory where Bacula Director temporarily saves files during job execution. PidDirectory: The directory where the Director saves its PID file (process identifier). This is used to track if the process is running. Maximum Concurrent Jobs: The maximum number of jobs that can run simultaneously. The default is 20. Password: Password used for authenticating the management console (bconsole) with the Director. Must match the one specified in the console’s configuration. Messages: Specifies the name of the message resource that determines how messages (errors, warnings, events) are handled. Common values: Daemon, Standard, Custom. DirAddress: The IP address the Director listens on. This can be 127.0.0.1 for local connections or an external IP. Catalog Configuration By default, Bacula comes with its own PostgreSQL instance on the same host, and in that case, database connection settings don’t need changes. But if you're deploying the database separately (recommended for production), the address, username, and password must be specified in the Catalog block: Catalog { Name = MyCatalog dbname = "bacula"; DB Address = "localhost"; dbuser = "bacula"; dbpassword = "StrongPassword4747563" } Explanation of parameters: dbname: The name of the database used by Bacula (default is bacula). The database must already exist (when deployed separately). DB Address: Host address where the DBMS is deployed. Use IP or a domain name. 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Exclude { File = /var/lib/bacula ... } Pool Configuration The Pool block defines a group of volumes (storage units) used for backup. Pools help manage how data is stored, rotated, and deleted. Pool { Name = Default Pool Type = Backup Recycle = yes AutoPrune = yes Volume Retention = 7 days Maximum Volume Bytes = 10G Maximum Volumes = 2 } Explanation of parameters: Name: The pool's name, here it's Default. Pool Type: Defines the pool's function: Backup: Regular backups. Archive: Long-term storage. Cloning: Data duplication. Recycle: Indicates whether volumes can be reused once they're no longer needed (yes or no). AutoPrune: Enables automatic cleanup of expired volumes. Volume Retention: How long (in days) to retain data on a volume. After 7 days, the volume becomes eligible for reuse. Maximum Volume Bytes: The max size for a volume. If it exceeds 10 GB, a new volume is created (if allowed). Maximum Volumes: Limits the number of volumes in the pool. Here, it's 2. Older volumes are recycled when the limit is hit (if Recycle = yes). Validating Configuration and Restarting Bacula After making all changes, check the bacula-dir.conf file for syntax errors: /usr/sbin/bacula-dir -t -c /etc/bacula/bacula-dir.conf If the command output is empty, there are no syntax errors. If there are errors, the output will specify the line number and error description. Restart the Bacula Director service: systemctl restart bacula-director Configuring Bacula Storage The next step is configuring Bacula Storage, where the backup files will be stored. 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Maximum Concurrent Jobs: Maximum number of jobs the storage daemon can handle simultaneously. SDAddress: IP address the Storage Daemon is available at. This can be an IP or a domain name. Since in our case the Storage Daemon runs on the same server as the Director, we use localhost. The next block to configure is Device, which defines the storage device where backups will be written. The device can be physical (e.g., a tape drive) or logical (e.g., a directory on disk). For testing, one Device block will suffice. By default, bacula-sd.conf may contain more than one Device block, including a Virtual Autochanger — a mechanism that emulates a physical autochanger (used for managing tapes or other media). It lets you manage multiple virtual volumes (typically as disk files) just like real tapes in a tape library. Locate the Autochanger block and remove the FileChgr1-Dev2 value from the Device parameter: Autochanger { Name = FileChgr1 Device = FileChgr1-Dev1 Changer Command = "" Changer Device = /dev/null } Next, in the Device block below, specify the full path to the directory we previously created for storing backup files (/srv/backup) in the Archive Device parameter: Device { Name = FileChgr1-Dev1 Media Type = File1 Archive Device = /srv/backup LabelMedia = yes; Random Access = Yes; AutomaticMount = yes; RemovableMedia = no; AlwaysOpen = no; Maximum Concurrent Jobs = 5 } Any blocks referencing FileChgr2 and FileChgr1-dev2 should be deleted: Explanation of the parameters: Autochanger Block: Name: Identifier for the autochanger (you can have multiple). Device: Name of the device linked to this autochanger—must match the Device block name. Changer Command: Script or command used to manage the changer. An empty value ("") means none is used—suitable for virtual changers or simple setups. Changer Device: Refers to the device tied to the autochanger, typically for physical devices. Device Block: Name: Identifier for the device. Media Type: Media type associated with the device. Must match the Pool block media type. Archive Device: Full path to the device or directory for storing backups; /srv/backup in this case. LabelMedia: Whether Bacula should auto-label new media. Random Access: Whether random access is supported. AutomaticMount: Whether to auto-mount the device when used. RemovableMedia: Specifies if the media is removable. AlwaysOpen: Whether the device should always stay open. Maximum Concurrent Jobs: Maximum number of simultaneous jobs using this device. Since we previously specified the directory for backup storage, create it: mkdir -p /srv/backup Set the ownership to the bacula user: chown bacula:bacula /srv/backup Next, check the config file for syntax errors: /usr/sbin/bacula-sd -t -c /etc/bacula/bacula-sd.conf If there are no syntax errors, the output will be empty. Otherwise, it will indicate the line number and description of any error. Restart the storage daemon: systemctl restart bacula-sd Creating a Backup Backups in Bacula are created using the bconsole command-line tool. Launch the utility: bconsole If it connects to the Director component successfully, it will display 1000 OK. Before running a backup, you can check the status of all components by entering the command: status This will display a list of the five Bacula system components. To check them all, enter 6. To initiate a backup, enter the command: run From the list, choose the BackupClient1 option (your client name might differ based on previous config), by typing 1. After selecting the option, you’ll see detailed info about the backup operation. You’ll then be prompted with three choices: yes — start the backup process; mod — modify parameters before starting; no — cancel the backup. If you enter mod, you’ll be able to edit up to 9 parameters. To proceed with the backup, type yes. To view all backup and restore jobs and their statuses: list jobs In our case, a backup with Job ID 1 was created: list jobid=1 If the status is T, the backup was successful. Possible statuses in the "Terminated Jobs" column: T (Success) — Job completed successfully. E (Error) — Job ended with an error. A (Canceled) — Job was canceled by the user. F (Fatal) — Job ended due to a critical error. R (Running) → Terminated — Job completed (may be successful or not). 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18 July 2025 · 14 min to read
Linux

Installing Arch Linux in a Cloud Environment

Arch Linux is a lightweight and flexible Linux distribution that provides users with extensive opportunities for customizing and optimizing their systems. It includes a minimal amount of preinstalled software and offers a console-based interface. In most cases, it is used by experienced users: professional developers, system administrators, or hackers. This is due to the complexity of its installation and subsequent configuration, which involves adding the required packages and components to the system. However, these difficulties are justified, because in the end the user gets exactly the system and services they need. In this article, we will explain how to install Arch Linux on your cloud server and perform its basic configuration. Advantages of Arch Linux It is worth noting that Arch Linux is ideally suited as an OS for a cloud server due to its low resource requirements. This distribution also has several other advantages: System UpdatesArch Linux updates automatically when a new OS version is released. Software InstallationPackages can be downloaded both over the network and from a local disk. In addition, the installed software does not need to be specifically compatible with Arch Linux. Rich RepositoriesArch Linux offers a wide variety of packages. Today, there are over 12,000 packages in the official repositories alone. In the community repository, there are even more — over 83,000. Up-to-date DocumentationThe official Arch Linux documentation is actively updated to reflect the latest changes and innovations. This ensures accurate and relevant system information. Active CommunityThis distribution has an active user community ready to help and share their experience. There are many forums, wikis, and repositories where you can find detailed instructions and guides for installation, configuration, and troubleshooting. 1. Preparing for Installation To follow this guide and install Arch Linux, you will need: A cloud server with any operating system (in our case, Debian 11); A link to the Arch Linux image from an official source; An additional disk, which you can attach under the Plan tab in the control panel. Step 1. To install Arch Linux on the server, you must first upload its installation image from an official source in .iso format. For example: wget https://mirror.rackspace.com/archlinux/iso/2025.06.01/archlinux-2025.06.01-x86_64.iso Step 2. Next, add a new disk where the installation image will be stored. It will appear in the system as /dev/sdb. You can specify the minimum disk size. Step 3. Write the installation image to the new disk: dd if=archlinux-2025.06.01-x86_64.iso of=/dev/sdb The writing process will take some time. When finished, verify it with the following command: fdisk -l In the output, you will see that the installation image has been written to the new disk, creating two necessary partitions. Step 4. After writing the installation image, proceed to boot from it. To do this, go to the Access tab and boot the server from the recovery disk. Open the console in the control panel.  Step 5. In the console window, go to the Boot existing OS menu item and press Tab on your keyboard. This will allow you to edit the text at the bottom of the screen. Here, you need to manually replace hd0 with hd1, as shown in the figure below. After that, press Enter to launch the installation program. Step 6. In the system bootloader that appears, select the first option. 2. Partitioning the Disk Now we can partition the main disk (sda). In our case, there will be 3 partitions: a 300 MB UEFI partition (type EFI), a 700 MB swap partition (type Linux swap), and a main filesystem partition taking up all remaining space (type Linux). In your own installation, the number and size of partitions may differ depending on your requirements. Make sure there are no important files on the server’s disk, because it will be formatted later. You may also wish to back it up to preserve important data. Step 1. First, check whether there are any files on the disk you need to save: lsblk The screenshot below shows the list. For creating the described partitions, we will use a 25 GB disk — sda. It currently has Debian 11 installed, which does not contain important files. Step 2. To partition the disk, enter the following command: cfdisk /dev/sda Step 3. In the window that opens, you need to delete all existing partitions. To do this, select a partition and use the Delete button in the lower menu. Step 4. Next, select the New button in the lower menu to create a new partition. Step 5. Then specify the size of the partition to be created. In our case, this is 300 MB for UEFI. Step 6. In the next window, choose Primary. Step 7. The partition is now created, and you need to specify its type. Go to the Type menu and select EFI. Step 8. Now move to the Free space and create 2 more partitions, repeating steps 4 through 7. Partition details were listed at the beginning of this chapter. Step 9. Once all partitions have been created, go to the Write button and select it. To confirm, type yes in the field that appears. Step 10. Partitioning is now complete. To exit the tool, select the Quit button in the lower menu. Step 11. You can verify your work using the lsblk command again. Check in the output that all changes have been successfully applied. 3. Formatting and Mounting the Created Partitions At this stage, the created partitions will be formatted and mounted. Remember, all data will be erased in this process! Step 1. For the first partition, format it using the following command: mkfs.fat -F32 /dev/sda1 This command will create a FAT32 filesystem, which is the recommended format for the UEFI partition. Step 2. Next, assign it a mount point: mkdir /mnt/efi mount /dev/sda1 /mnt/efi Step 3. For the second partition, perform special formatting: mkswap /dev/sda2 Step 4. Then activate the swap partition: swapon /dev/sda2 Step 5. Finally, format the system’s root partition: mkfs.ext4 /dev/sda3 Step 6. After formatting, create its mount point: mount /dev/sda3 /mnt After completing the formatting and mounting, your partitions will be ready for installing and configuring Arch Linux and its main components. 4. Installing the Main Arch Linux Components Step 1. First, let’s install the OS and its core components: pacstrap /mnt base linux grub openssh nano dhcpcd Step 2. Once the installation finishes, you need to generate the fstab file: genfstab -U /mnt >> /mnt/etc/fstab Generating the fstab file makes partition mounting management easier and ensures automatic and consistent mounting at system startup. 5. System Configuration Step 1. To configure Arch Linux after installation, you need to chroot into the OS without rebooting: arch-chroot /mnt Step 2. First, install the nano text editor: pacman -S nano Step 3. Uncomment the encoding for English in the relevant file (you would edit locale.gen): nano /etc/locale.gen Uncomment the line for en_US.UTF-8. After this, save the changes and exit nano, then generate the locales: locale-gen To enable the English language, execute: echo "LANG=en_US.UTF-8" > /etc/locale.conf Step 4. At this step, set up the system clock. For example:  ln -sf /usr/share/zoneinfo/Europe/Nicosia /etc/localtime The region is set. Now synchronize the hardware clock: hwclock --systohc Step 5. Next, set the hostname for your system: echo "hostname" > /etc/hostname Step 6. As the second-to-last step, set the root password. Run: passwd You will be prompted to enter and confirm the password. Step 7. Lastly, set up the previously installed GRUB bootloader to boot the server: grub-install --target=i386-pc /dev/sda Then create the GRUB configuration file: grub-mkconfig -o /boot/grub/grub.cfg This command will automatically configure GRUB. Step 8. Arch Linux is now successfully installed. Exit the chroot: exit Then go to the Access tab in your control panel and switch the server to standard boot mode. After that, click Save and Reboot. You can remove the additional disk after this step. Step 9. The system will boot, but it is not ready for use yet. First, connect to the server and enable the DHCP client daemon: systemctl enable dhcpcd Then start it: systemctl start dhcpcd Make sure the service shows the status active (running). Step 10. Next, configure the SSH connection. First, create a backup of the sshd configuration: cp /etc/ssh/sshd_config /etc/ssh/backup.sshdconf Then set PermitRootLogin to Yes in the /etc/ssh/sshd_config file: nano /etc/ssh/sshd_config Finally, enable the SSH daemon: systemctl enable sshd And start it: systemctl start sshd When checking with systemctl status sshd, the service should show active (running) status. Don’t forget to add and configure SSH keys before connecting to the server. 6. Additional Configuration The installation is complete, but you can also perform additional system configuration by reviewing the official Arch Linux setup documentation. To install packages, use the command: pacman -S package_name To update the system, use: pacman -Suy Conclusion In this guide, we reviewed the process of installing Arch Linux on your cloud server and performed its basic configuration. We used a temporary Debian 11 OS and an additional disk for the installation image. By following these steps, you can create a powerful and flexible virtual environment for developing, testing, and running applications based on Arch Linux.
03 July 2025 · 8 min to read

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