Key Linux Commands for DevOps Beginners

Linux is an open-source operating system that is widely used in DevOps environments. As a DevOps engineer, knowing the Linux command line is crucial for efficient system administration and management. In this blog, we have compiled a list of important Linux commands that every DevOps engineer should know.

File System Hierarchy

/: This is the top-level directory in Linux, also known as the root directory.
/root: This is the home directory for the root user.
/home: This is the home directory for other users.
/boot: This directory contains bootable files for Linux.
/etc: This directory contains all configuration files.
/usr: By default, software is installed in this directory.
/bin: This directory contains commands used by all users.
/sbin: This directory contains commands used only by the root user.

Example -

Here are some examples of navigating and using the file system hierarchy in Linux:

/ - Top level directory

Command: cd /
Output:

bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

This is the top level directory in Linux, also known as the root directory. It contains all the other directories and files on the system.

/root - Home directory for root user

Command: cd /root
Output:

Desktop  Documents  Music  Pictures  Public  Videos

This is the home directory for the root user. It contains the root user's personal files and directories.

/home - Home directory for other users

Command: cd /home
Output:

user1  user2  user3

This directory contains the home directories for all users on the system, except for the root user.

/boot - Bootable files for Linux

Command: cd /boot
Output:

config-4.15.0-72-generic  grub  initrd.img-4.15.0-72-generic  System.map-4.15.0-72-generic  vmlinuz-4.15.0-72-generic

This directory contains the bootable files for Linux, including the kernel and initrd images.

/etc - Configuration files

Command: cd /etc
Output:

adduser.conf  aliases  apache2  apt  bash.bashrc  bind  cron.d  dbus-1  default  dhcp  fstab  group  hosts  init  inittab  issue  ldap  logrotate.conf  lsb-release  mailcap  mime.types  modprobe.d  modules  mtab  networks  nsswitch.conf  pam.conf  passwd  profile  protocols  resolv.conf  rpc  services  shadow  shells  skel  ssh  ssl  sysctl.conf  systemd  udev  useradd.conf  vim  xdg

This directory contains all the configuration files for the system, including user and group information, network settings, and system services.

/usr - Software installation directory

Command: cd /usr
Output:

bin  games  include  lib  lib64  libexec  local  sbin  share  src

This directory is where software is installed by default. It contains subdirectories for different types of software, such as bin for executable files and lib for libraries.

/bin - Commands used by all users

Command: cd /bin
Output:

bash  cat  chmod  chown  cp  date  dd  df  echo  grep  gzip  hostname  kill  ln  ls  mkdir  mknod  more  mount  mv  ping  ps  pwd  rm  rmdir  sed  sh  sleep  sort  tail  tar  touch  umount  uname  uniq  wc  which  xargs

This directory contains essential commands that are used by all users on the system.

/sbin - Commands used by root user

Command: cd /sbin
Output:

acpid  blkid  depmod  fdisk  fsck  grub-mkconfig  ifconfig  init  insmod  ip  lsmod  mke2fs  mkfs  mkswap  modinfo  modprobe  mount  poweroff  reboot  rmmod  route  runlevel  shutdown  swapoff  swapon  sysctl  tune2fs  umount

This directory contains system administration commands that are used by the root user.

Linux Basic Commands

cat (create & append file)
- Command: cat > file.txt
  - Output: Creates a new file called file.txt and opens it in the default editor.
  - Command: cat >> file.txt
  - Output: Appends to the existing file called file.txt.

Example:

        $ cat > file.txt
        Hello World!
        $ cat file.txt
        Hello World!
        $ cat >> file.txt
        This is appended text.
        $ cat file.txt
        Hello World!
        This is appended text.

touch (create blank file)

Command: touch file.txt
Output: Creates a new blank file called file.txt.

Example:

        $ touch file.txt
        $ ls
        file.txt

nano (create & edit file)

Command: nano file.txt
Output: Opens the file called file.txt in the nano editor.

Example:

        $ nano file.txt

This will open the nano editor where you can create and edit the file.

vi/vim (create & edit file)

Command: vi file.txt
Output: Opens the file called file.txt in the vi editor.

Example:

        $ vi file.txt

This will open the vi editor where you can create and edit the file.

ls (list)

Command: ls
Output: Lists the files and directories in the current directory.

Example:

        $ ls
        file1.txt  file2.txt  dir1  dir2

Command: ls -a
Output: Lists all files and directories, including hidden ones.

Example:

        $ ls -a
        .  ..  file1.txt  file2.txt  dir1  dir2  .hidden_file

Command: ls -la
Output: Lists all files and directories in a detailed format.

Example:

        $ ls -la
        total 12
        drwxr-xr-x  3 user user 4096 Aug 17 14:23 .
        drwxr-xr-x 10 user user 4096 Aug 17 14:23 ..
        -rw-r--r--  1 user user   12 Aug 17 14:23 file1.txt
        -rw-r--r--  1 user user   12 Aug 17 14:23 file2.txt
        drwxr-xr-x  2 user user 4096 Aug 17 14:23 dir1
        drwxr-xr-x  2 user user 4096 Aug 17 14:23 dir2
        -rw-r--r--  1 user user   12 Aug 17 14:23 .hidden_file

cd (change directory)

Command: cd dir1
Output: Changes the current directory to dir1.

Example:

        $ cd dir1
        $ pwd
        /home/user/dir1

pwd (print working directory)

Command: pwd
Output: Prints the current working directory.

Example:

        $ pwd
        /home/user

mkdir (create directory, multiple)

Command: mkdir dir1 dir2
Output: Creates two new directories called dir1 and dir2.

Example:

        $ mkdir dir1 dir2
        $ ls
        dir1  dir2

cp (copy)

Command: cp file1.txt file2.txt
Output: Copies the contents of file1.txt to file2.txt.

Example:

        $ cp file1.txt file2.txt
        $ cat file2.txt
        Hello World!

mv (move)

Command: mv file1.txt dir1
Output: Moves the file file1.txt to the directory dir1.

Example:

        $ mv file1.txt dir1
        $ ls dir1
        file1.txt

mv (rename)

Command: mv file1.txt file2.txt
Output: Renames the file file1.txt to file2.txt.

Example:

        $ mv file1.txt file2.txt
        $ ls
        file2.txt

rm (remove file)

Command: rm file1.txt
Output: Removes the file file1.txt.

Example:

        $ rm file1.txt
        $ ls

tree (see in tree structure)

Command: tree
Output: Displays the directory structure in a tree-like format.

Example:

        $ tree
        .
        |-- dir1
        |   |-- file1.txt
        |   |-- file2.txt
        |-- dir2
        |   |-- file3.txt
        |   |-- file4.txt
        |-- file5.txt

rm -rf (remove directory & recursive)

Command: rm -rf dir1
Output: Removes the directory dir1 and all its contents recursively.

Example:

        $ rm -rf dir1
        $ ls

grep (pick & print)

Command: grep "Hello" file1.txt
Output: Prints

Here are the Linux commands with examples:

less (see output)

Command: less file.txt
Output: Displays the contents of file.txt one screen at a time.

Example:

        $ less file.txt
        Hello World!
        This is a test file.
        ...

You can scroll through the file using the arrow keys or page up/down keys.

head (see top 10 lines)

Command: head file.txt
Output: Displays the first 10 lines of file.txt.

Example:

        $ head file.txt
        Hello World!
        This is a test file.
        Line 3
        Line 4
        Line 5
        Line 6
        Line 7
        Line 8
        Line 9
        Line 10

tail (see last 10 lines)

Command: tail file.txt
Output: Displays the last 10 lines of file.txt.

Example:

        $ tail file.txt
        Line 91
        Line 92
        Line 93
        Line 94
        Line 95
        Line 96
        Line 97
        Line 98
        Line 99
        Line 100

sort (display in Alphabetic/Numeric order)

Command: sort file.txt
Output: Displays the contents of file.txt in alphabetical order.

Example:

        $ sort file.txt
        Apple
        Banana
        Cat
        Dog
        Elephant
        ...

You can also use the -n option to sort in numeric order:

        $ sort -n file.txt
        1
        2
        3
        4
        5
        ...

User

Command: useradd username
Output: Creates a new user account with the specified username.

Example:

        $ useradd john

Group

Command: groupadd groupname
Output: Creates a new group with the specified groupname.

Example:

        $ groupadd admins

Soft Link (shortcut)

Command: ln -s file.txt link.txt
Output: Creates a soft link (shortcut) to file.txt called link.txt.

Example:

        $ ln -s file.txt link.txt
        $ ls -l
        lrwxr-xr-x  1 user user  9 Aug 17 14:23 link.txt -> file.txt

Hard Link (backup)

Command: ln file.txt backup.txt
Output: Creates a hard link (backup) to file.txt called backup.txt.

Example:

        $ ln file.txt backup.txt
        $ ls -l
        -rw-r--r--  2 user user  12 Aug 17 14:23 backup.txt
        -rw-r--r--  2 user user  12 Aug 17 14:23 file.txt

/tar (to pack)

Command: tar -cvf archive.tar file.txt
Output: Creates a tar archive of file.txt called archive.tar.

Example:

        $ tar -cvf archive.tar file.txt
        file.txt
        $ ls
        archive.tar

gz (to compress)

Command: gzip file.txt
Output: Compresses file.txt using gzip.

Example:

        $ gzip file.txt
        $ ls
        file.txt.gz

You can also use the -d option to decompress the file:

        $ gzip -d file.txt.gz
        $ ls
        file.txt

yum (to install)

Command: yum install package_name
Output: Installs the specified package using the yum package manager.

Example:

        $ yum install firefox
        Loaded plugins: fastestmirror, langpacks
        Resolving Dependencies
        --> Running transaction check
        ---> Package firefox.x86_64 0:68.0.1-1.el7 will be installed
        --> Finished Dependency Resolution

        Dependencies Resolved

        ================================================================================================
         Package          Arch           Version               Repository       Size
        ================================================================================================
        Installing:
         firefox          x86_64         68.0.1-1.el7          updates         80 M

        Transaction Summary
        ================================================================================================
        Install  1 Package

        Total download size: 80 M
        Installed size: 170 M
        Is this ok [y/N]: y
        Downloading packages:
        firefox-68.0.1-1.el7.x86_64.rpm                              |  80 MB   00:01
        Running transaction check
        Running transaction test
        Transaction test succeeded
        Running transaction
          Installing : firefox-68.0.1-1.el7.x86_64                                  1/1
          Verifying  : firefox-68.0.1-1.el7.x86_64                                  1/1

        Installed:
          firefox.x86_64 0:68.0.1-1.el7

        Complete!

wget (to download)

Command: wget url
Output: Downloads the file from the specified URL using wget.

Example:

        $ wget https://www.example.com/file.txt
        --2023-03-01 14:23:45--  https://www.example.com/file.txt
        Resolving www.example.com (www.example.com)... 93.184.216.34
        Connecting to www.example.com (www.example.com)|93.184.216.34|:443... connected.
        HTTP request sent, awaiting response... 200 OK
        Length: 12 [text/plain]
        Saving to: ‘file.txt’

        100%[======================================>] 12          --.-K/s   in 0s

        2023-03-01 14:23:45 (1.23 MB/s) - ‘file.txt’ saved [12/12]

File/Directory Permissions

Command: ls -l
Output: Displays the permissions of files and directories in the current directory.

Example:

        $ ls -l
        total 0
        -rw-r--r--  1 user user  12 Aug 17 14:23 file.txt
        drwxr-xr-x  2 user user 4096 Aug 17 14:23 dir1

chmod (permissions)

Command: chmod permissions file.txt
Output: Changes the permissions of file.txt to the specified permissions.

Example:

        $ chmod 755 file.txt
        $ ls -l
        total 0
        -rwxr-xr-x  1 user user  12 Aug 17 14:23 file.txt

chown (owner)

Command: chown user:group file.txt
Output: Changes the owner and group of file.txt to the specified user and group.

Example:

        $ chown user:group file.txt
        $ ls -l
        total 0
        -rwxr-xr-x  1 user group  12 Aug 17 14:23 file.txt

chgrp (group)

Command: chgrp group file.txt
Output: Changes the group of file.txt to the specified group.

Example:

        $ chgrp group file.txt
        $ ls -l
        total 0
        -rwxr-xr-x  1 user group  12 Aug 17 14:23 file.txt

hostname (to see hostname)

Command: hostname
Output: Displays the hostname of the system.

Example:

        $ hostname
        localhost

ifconfig (to get ip address)

Command: ifconfig
Output: Displays the network interface configuration, including the IP address.

Example:

        $ ifconfig
        eth0      Link encap:Ethernet  HWaddr 00:11:22:33:44:55
                  inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
                  UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
                  RX packets:1000 errors:0 dropped:0 overruns:0 frame:0
                  TX packets:500 errors:0 dropped:0 overruns:0 carrier:0
                  collisions:0 txqueuelen:1000
                  RX bytes:64000 (62.5 KiB)  TX bytes:32000 (31.2 KiB)

cat /etc/rele (to get os version)

Command: cat /etc/*release*
Output: Displays the OS version information.

Example:

        $ cat /etc/*release*
        NAME="CentOS Linux

apt get install httpd (to install package)

Command: apt-get install httpd
Output: Installs the Apache HTTP server package using apt-get.

Example:

        $ apt-get install httpd
        Reading package lists... Done
        Building dependency tree
        Reading state information... Done
        The following NEW packages will be installed:
          httpd
        0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
        Need to get 1,342 kB of archives.
        After this operation, 3,942 kB of additional disk space will be used.
        Get:1 http://archive.ubuntu.com/ubuntu xenial/main amd64 httpd amd64 2.4.18-2ubuntu3 [1,342 kB]
        Fetched 1,342 kB in 1s (1,342 kB/s)
        Selecting previously unselected package httpd.
        (Reading database ... 186,255 files and directories currently installed.)
        Preparing to unpack .../httpd_2.4.18-2ubuntu3_amd64.deb ...
        Unpacking httpd (2.4.18-2ubuntu3) ...
        Processing triggers for ureadahead (0.100.0-19) ...
        Processing triggers for systemd (229-4ubuntu21) ...
        Setting up httpd (2.4.18-2ubuntu3) ...

yum update httpd (to upgrade package)

Command: yum update httpd
Output: Upgrades the Apache HTTP server package using yum.

Example:

        $ yum update httpd
        Loaded plugins: fastestmirror, langpacks
        Resolving Dependencies
        --> Running transaction check
        ---> Package httpd.x86_64 0:2.4.6-40.el7 will be updated
        ---> Package httpd.x86_64 0:2.4.6-45.el7 will be an update
        --> Finished Dependency Resolution

        Dependencies Resolved

        ================================================================================================
         Package          Arch           Version               Repository       Size
        ================================================================================================
        Updating:
         httpd            x86_64         2.4.6-45.el7          updates         1.2 M

        Transaction Summary
        ================================================================================================
        Upgrade  1 Package

        Total download size: 1.2 M
        Is this ok [y/N]: y
        Downloading packages:
        httpd-2.4.6-45.el7.x86_64.rpm                              | 1.2 MB   00:01
        Running transaction check
        Running transaction test
        Transaction test succeeded
        Running transaction
          Updating   : httpd-2.4.6-45.el7.x86_64                                  1/2
          Cleanup    : httpd-2.4.6-40.el7.x86_64                                  2/2

        Updated:
          httpd.x86_64 0:2.4.6-45.el7

        Complete!

yum remove httpd (to uninstall package)

Command: yum remove httpd
Output: Uninstalls the Apache HTTP server package using yum.

Example:

        $ yum remove httpd
        Loaded plugins: fastestmirror, langpacks
        Resolving Dependencies
        --> Running transaction check
        ---> Package httpd.x86_64 0:2.4.6-45.el7 will be erased
        --> Finished Dependency Resolution

        Dependencies Resolved

        ================================================================================================
         Package          Arch           Version               Repository       Size
        ================================================================================================
        Removing:
         httpd            x86_64         2.4.6-45.el7          @updates         3.9 M

        Transaction Summary
        ================================================================================================
        Remove  1 Package

        Installed size: 3.9 M
        Is this ok [y/N]: y
        Running transaction check
        Running transaction test
        Transaction test succeeded
        Running transaction
          Erasing    : httpd-2.4.6-45.el7.x86_64                                  1/1

        Removed:
          httpd.x86_64 0:2.4.6-45.el7

        Complete!

yum list installed (to see installed packages)

Command: yum list installed
Output: Lists all installed packages using yum.

Example:

        $ yum list installed
        Loaded plugins: fastestmirror, langpacks
        Installed Packages
        GConf2.x86_64                  3.2.6-8.el7                  @anaconda
        GeoIP.x86_64                   1.5.0-11.el7                 @anaconda
        ModemManager.x86_64            1.6.0-2.el7                  @anaconda
        NetworkManager.x86_64          1:1.10.2-14.el7              @anaconda
        ...

service httpd status (to see status)

Command: service httpd status
Output: Displays the status of the Apache HTTP server service.

Example:

        $ service httpd status
        Redirecting to /bin/systemctl status  httpd.service
        ● httpd.service - The Apache HTTP Server
           Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
           Active: active (running) since Thu

service httpd status (to see status)

Command: service httpd status
Output: Displays the status of the Apache HTTP server service.

Example:

        $ service httpd status
        Redirecting to /bin/systemctl status  httpd.service
        ● httpd.service - The Apache HTTP Server
           Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
           Active: active (running) since Thu 2023-02-16 14:30:12 EST; 1h 15min ago
          Process: 1234 ExecStart=/usr/sbin/httpd $OPTIONS -DFOREGROUND (code=exited, status=0/SUCCESS)
         Main PID: 1235 (httpd)
           Status: "Total requests: 100; Current requests/sec: 0; Current traffic:   0 B/sec"
           CGroup: /system.slice/httpd.service
                   └─1235 /usr/sbin/httpd -DFOREGROUND

Explanation: The output shows that the Apache HTTP server service is currently running and has been active for 1 hour and 15 minutes.

service httpd start (to start service)

Command: service httpd start
Output: Starts the Apache HTTP server service.

Example:

        $ service httpd start
        Redirecting to /bin/systemctl start  httpd.service

Explanation: The command starts the Apache HTTP server service.

service httpd reload (to restart service)

Command: service httpd reload
Output: Reloads the Apache HTTP server service.

Example:

        $ service httpd reload
        Redirecting to /bin/systemctl reload  httpd.service

Explanation: The command reloads the Apache HTTP server service, which reloads the configuration files without restarting the service.

service httpd restart (to restart service)

Command: service httpd restart
Output: Restarts the Apache HTTP server service.

Example:

        $ service httpd restart
        Redirecting to /bin/systemctl restart  httpd.service

Explanation: The command restarts the Apache HTTP server service, which stops and starts the service again.

chkconfig httpd on (to start service permanently)

Command: chkconfig httpd on
Output: Enables the Apache HTTP server service to start automatically on boot.

Example:

        $ chkconfig httpd on

Explanation: The command enables the Apache HTTP server service to start automatically on boot.

chkconfig httpd off (to stop service permanently)

Command: chkconfig httpd off
Output: Disables the Apache HTTP server service from starting automatically on boot.

Example:

        $ chkconfig httpd off

Explanation: The command disables the Apache HTTP server service from starting automatically on boot.

Redirection (redirecting output)

Redirection is a feature in Linux that allows you to redirect the output of a command to a file or another command.

>: Redirects the output to a file, overwriting the file if it already exists.
>>: Redirects the output to a file, appending to the file if it already exists.
2>: Redirects the error output to a file.
2>>: Redirects the error output to a file, appending to the file if it already exists.
&>: Redirects both the output and error output to a file.
|: Pipes the output to another command.

Examples:

ls > file.txt: Redirects the output of the ls command to a file called file.txt.
ls >> file.txt: Appends the output of the ls command to a file called file.txt.
ls 2> error.txt: Redirects the error output of the ls command to a file called error.txt.
ls 2>> error.txt: Appends the error output of the ls command to a file called error.txt.
ls &> output.txt: Redirects both the output and error output of the ls command to a file called output.txt.
ls | grep keyword: Pipes the output of the ls command to the grep command, which searches for the keyword in the output.

Redirection (redirecting output)

Redirection is a feature in Linux that allows you to redirect the output of a command to a file or another command.

>: Redirects the output to a file, overwriting the file if it already exists.
>>: Redirects the output to a file, appending to the file if it already exists.
2>: Redirects the error output to a file.
2>>: Redirects the error output to a file, appending to the file if it already exists.
&>: Redirects both the output and error output to a file.
|: Pipes the output to another command.

Examples:

ls > file.txt: Redirects the output of the ls command to a file called file.txt.
- Output: The output of the ls command is written to file.txt.
ls >> file.txt: Appends the output of the ls command to a file called file.txt.
- Output: The output of the ls command is appended to file.txt.
ls 2> error.txt: Redirects the error output of the ls command to a file called error.txt.
- Output: The error output of the ls command is written to error.txt.
ls 2>> error.txt: Appends the error output of the ls command to a file called error.txt.
- Output: The error output of the ls command is appended to error.txt.
ls &> output.txt: Redirects both the output and error output of the ls command to a file called output.txt.
- Output: Both the output and error output of the ls command are written to output.txt.
ls | grep keyword: Pipes the output of the ls command to the grep command, which searches for the keyword in the output.
- Output: The output of the ls command is piped to the grep command, which searches for the keyword.

which (to see package installed or not)
- Command: which package_name
Output: Displays the path to the executable file of the package if it is installed.

Example:
```
$ which python
/usr/bin/python
```
Explanation: The output shows that the python package is installed and the executable file is located at /usr/bin/python.

sudo (to get root privileges)
Command: sudo command
Output: Executes the command with root privileges.

Example:

        $ sudo apt-get install firefox

Explanation: The command installs the firefox package using the apt-get command with root privileges.

whoami (to see user)

Command: whoami
Output: Displays the username of the current user.

Example:

        $ whoami
        user123

Explanation: The output shows that the current user is user123.

Note: The whoami command is similar to the id command, but it only displays the username, whereas id displays more information about the user, including the user ID, group ID, and group membership.

Here are the Linux `find` commands with examples and outputs:

find -type f (to see all files in current directory)

Command: find . -type f
Output: Displays all files in the current directory and its subdirectories.

Example:

        $ find . -type f
        ./file1.txt
        ./file2.txt
        ./dir1/file3.txt
        ./dir1/file4.txt

Explanation: The output shows all files in the current directory (file1.txt and file2.txt) and its subdirectory (dir1) with files (file3.txt and file4.txt).

find -type d (to see all directories in current directory)

Command: find . -type d
Output: Displays all directories in the current directory and its subdirectories.

Example:

        $ find . -type d
        .
        ./dir1
        ./dir1/dir2

Explanation: The output shows all directories in the current directory (.) and its subdirectories (dir1 and dir1/dir2).

find / -type f (to see all files under top level root directory)

Command: find / -type f
Output: Displays all files under the top-level root directory (/).

Example:

        $ find / -type f
        /bin/bash
        /bin/cat
        /bin/ls
        /etc/passwd
        /etc/group
        ...

Explanation: The output shows all files under the top-level root directory (/), including system files and configuration files.

find / -type d (to see all directories under top level root directory)

Command: find / -type d
Output: Displays all directories under the top-level root directory (/).

Example:

        $ find / -type d
        /
        /bin
        /etc
        /etc/init.d
        /usr
        /usr/bin
        ...

Explanation: The output shows all directories under the top-level root directory (/), including system directories and subdirectories.

find / -type f -name <file_name> (to search specific file under top level root directory)

Command: find / -type f -name file_name
Output: Displays the path to the specific file under the top-level root directory (/).

Example:

        $ find / -type f -name passwd
        /etc/passwd

Explanation: The output shows the path to the passwd file under the top-level root directory (/etc/passwd).

find / -type d -name <dir_name> (to search specific dir under top level root directory)

Command: find / -type d -name dir_name
Output: Displays the path to the specific directory under the top-level root directory (/).

Example:

        $ find / -type d -name etc
        /etc

Explanation: The output shows the path to the etc directory under the top-level root directory (/etc).

Here are the commands in a single block:

        $ find . -type f
        ./file1.txt
        ./file2.txt
        ./dir1/file3.txt
        ./dir1/file4.txt

        $ find . -type d
        .
        ./dir1
        ./dir1/dir2

        $ find / -type f
        /bin/bash
        /bin/cat
        /bin/ls
        /etc/passwd
        /etc/group
        ...

        $ find / -type d
        /
        /bin
        /etc
        /etc/init.d
        /usr
        /usr/bin
        ...

        $ find / -type f -name passwd
        /etc/passwd

        $ find / -type d -name etc
        /etc

Note: The find command is a powerful tool for searching files and directories in Linux. The -type option specifies the type of file or directory to search for, and the -name option specifies the name of the file or directory to search for.