Manage your Linux Server via the Command Line Interface
Introduction
When working with cloud-based servers, you should master the basic Linux commands to perform administrative tasks. These commands are important when installing applications, monitoring server resources, managing the file system, and more.
Although there are many GUI-based applications that you can use to manage your server, the command-line interface is free, fast, easy to use. It offers more control, especially when you're remotely connected to your server via an OpenSSH Client. In this guide, you'll learn how to use the most powerful and popular Linux commands on your server.
Prerequisites
To complete this tutorial, you need:
- A Vultr Linux server.
- A non-root user with sudo access.
- An OpenSSH Client.
1. Linux Server Administration Commands
SSH to your server to run the following Linux administration commands.
sudo
The sudo command stands for superuser do. It allows you to run Linux commands with escalated privileges of the root user. You should pass sudo and the command name in one line as shown below.
You can learn more about sudo by reading the man page.
See more articles about sudo.
date
Run the date command to display or set the current date and time on your server.
To see the current date:
To set the date, use the `-s' parameter. For example:
You can learn more about date by reading the man page.
reboot
The reboot command restarts your server.
You'll lose your SSH connection and need to reconnect to the server after the operating system reboots. You can learn more about reboot by reading the man page.
wget
Download files from the web using the wget command. For instance, to download http://www.example.com/index.html:
To specify the output filename, use the `-O' parameter:
You can learn more about wget by reading the man page.
history
See the list of commands that you've previously run by using the history command.
To re-execute a command from your history list, use the ! symbol followed by a command.
!n : Refer to a command from your history list. For command number 109:
!-n : Refer to the current command minus n. For the previous command:
!! : Refer to the previous command. This is a synonym for
!-1.
There are several other options, search patterns, and substitutions available. See the man page for more information.
clear
If your terminal screen is overcrowded, run the clear command to reset the screen.
2. Linux File Management Commands
Use the commands below to manage directories and files in your Linux server.
pwd
In Linux, pwd is an acronym for print working directory. This command retrieves the path of your current working directory starting from root /.
mkdir
The mkdir stands for make directory. It allows you to create directories, which are also called folders in other operating systems.
Create a sample directory in your current location.
In most cases, you'll use the mkdir command with the -p flag. This option tells Linux to create parent directories along the way if they don't exist.
For instance, if you attempt to run the command below without the -p flag, it should fail.
Output.
However, if you use the -p flag, the command will create both the sample and abc directories if they don't exist.
The Linux mkdir command is handy when creating directories for running multiple websites on your server, as shown below.
cd
You can navigate to another directory by using the cd command which stands for change directory. For instance, cd to the new sample directory.
Run the pwd command to see if you've switched to the new directory.
Output.
To move up one level in the directory structure, use the cd .. command.
To navigate back to your home directory, use the cd command with the tilde(~) character.
ls
Use the Linux ls command to print a list of files in a directory. The output includes other sub-directories as well.
Output.
The ls command has different options that you can use to format the output. For instance, use the -l flag to show the list of files, including their sizes, time of modification, current owners, and permissions.
Output.
You can also use the h flags to display the sizes of the files in a human-readable format.
Output.
To display hidden files, pass the `a' flag.
Output.
touch
Use the touch command to change a files' last access date without modifying the contents. If the file does not exist, it will create an empty file with zero length. This is useful when you don't have content to put into the file at the creation time.
Confirm the success of the touch command by running the ls -lh command.
Output.
mv
The mv command allows you to move a file or a directory to another location. You can also use it to rename files. Rename the sample_file.txt to sample_file.bk.
Move the new sample_file.bk file to the /tmp directory.
rmdir
The rmdir stands for remove directory. You can use it to delete empty directories. Create a sample_2 directory and delete it.
rm
Use the rm command to delete files and non-empty directories. You should be careful when executing this command since it can break applications or render your system useless.
Delete the sample_file.bk in the /tmp directory.
To delete a directory and its contents, use the -r option. This allows you to delete the directory contents recursively. Create a sample_3 directory and a sample_4 sub-directory and delete them.
cp
In Linux, you can copy files and directories using the cp command. Normally, you need to specify the source and destination of the files.
Create a sample_2.txt file and copy it over to the /tmp directory.
This command is useful when tweaking settings on the base configuration files. Copy the default file to a new location with a new name to avoid losing the default settings.
For instance, before configuring the Apache virtual host file, create a backup copy so that you can restore the file in case you run into problems.
chown
The chown command allows you to change the ownership of directories and files in your server. For instance, when you create directories as a superuser using the sudo command, the root user owns the directories. Therefore, to navigate between the new directories without permission issues, you should take ownership of the new directories by executing the chown command.
For instance, create the directory below.
Take ownership of the new directory as the current user.
Also, you can assign ownership of the new directories to another user. For instance, www-data.
chmod
The chmod command allows you to change read, write, and execute permissions for files and directories. Normally, you should use this command alongside the following permission numbers:
- 0: No Permissions
- 1: Execute permissions
- 2: Write permissions
- 3: Execute and write permissions
- 4: Read permissions
- 5: Read and execute permissions
- 6: Write and read permissions
- 7: Full permissions (Read, write, and execute permissions).
The basic syntax for the chmod command is.
For instance, to assign john full permissions to the /var/www/example.net directory and deny anyone from accessing it, execute.
To give the user john full permissions(7) and assign only read and execute(5) permission to the group and the rest of the users, execute.
There are several other options available for chmod; please see the man file for more information.
cat
The cat (concatenate) command is useful when you want to read the content of a file and display the data in your shell window. For instance, use the cat command to display the content of your .bash_history file.
You can also display the content of multiple files using the cat command.
tail
Use the tail command to display the last parts of a file. This command is useful when you want to read log files to troubleshoot applications. To avoid displaying lots of content on the screen, specify the number of lines that you want to display when running the command.
Use the -f (follow) parameter to keep the file open and display any updates. This is useful when monitoring a log file.
3. User Management Commands
You can check your current username, create new users, and change their passwords using the following Linux shell commands.
whoami
Use the whoami command to check your current username.
Output.
adduser
The adduser command is useful for creating user accounts in your system. This command should be run by root or a sudo user. For instance, create a user named mary.
Follow the on-screen prompts to finalize setting up the account for the user.
passwd
You can change the password of a user by executing the passwd command. For instance, to change the password for user mary, run the command below.
Enter and confirm the new password to update the user account.
4. Memory, Disk, and CPU Management Commands
Use the following commands to monitor your Linux server's memory, disk usage, and CPU load.
free
To view the available RAM, use the free command. Pass the -h option to display the figures in a human-readable format.
Output.
du
The du command stands for disk usage. The utility allows you to gain disk usage information on your system.
Output.
df
Use the df(disk free) command to display the total and available space in your system.
Output.
top
To display the active Linux processes running in your system, use the top command.
Output.
5. File Searching Commands
Linux has five file searching commands: whereis, locate, which, type, and find. Each of them has its own characteristics and is designed for particular search scenarios.
whereis
The whereis command is used to search binary files, source code, and the online manual pages at several standard install directories for any program name specified.
Because whereis does not search every location on your system, any files out of these specific directories will not be found. For the same reason, you will get your search result quickly, whether found or not.
Also, it will not search for those commands which are built directly into the shell.
For example, if you want to find info about the ls command, run the following command on your terminal:
You will get some feedback like:
In the result, /bin/ls is the binary you want to locate, the other two are manpages for the ls program, and no source code for the ls program was found.
locate
The locate command is used to find files by name with the help of a database (/var/lib/mlocate/mlocate.db). This database is a snapshot of the layout of your filesystem. Any records in this database that match your query will be listed in the search result. By default, the locate command will use your query to match any part of the whole name of each record, including the pathname. Therefore, the number of matched files in the search result could be more than you expected.
As the database becomes outdated, the search result of the locate command becomes less accurate. You may notice files that no longer exist, or you won't see matches for newly-created files. By default, the mlocate.db database is automatically updated once a day. You can use the updatedb command to manually update it.
The search speed is very fast because the search is performed on the database instead of the filesystem.
If you run the following command:
You will get many records instead of your expected result.
In order to make the search result more accurate, you can use the -b flag to restrict the search range, using your query to match only the basename of each record:
This time, you will get the location of each file exactly called ls on your filesystem:
which
The which command will search for the command you specified in the environment variable PATH value and return the first result by default. If you are querying an alias, the which command will determine the actual command for the alias before performing your search.
The which command is also very fast because of its simplicity.
The usage of the which command is simple:
If you want to show all of the matched commands instead of the first one, use the `-a' flag:
Here is an example for searching for a command that has been aliased:
The search result would be:
type
By default, the type command will indicate how a command name would be interpreted. Possible results include an alias, a keyword, a function, a builtin, or a file. Just like the whereis command, the type command will only search in several standard install directories to answer your query.
Some examples for typing different commands:
A shell builtin command:
A binary file on the filesystem:
An alias:
find
The ' find ' command is the most powerful among the five file searching commands introduced in this tutorial. Unfortunately, it is also the slowest one. Unlike the other four commands, the find command will search for your file on the entire filesystem, one i-node by one i-node. With the find command, you can use sophisticated query criteria to find every file you need and execute actions on the files found.
Search criteria for the find command is too sophisticated to explain in such a short article; here are a few examples instead.
Basic format of the find command:
To find all files in the working directory and all of its sub-directories:
To find a file called aaa in your home directory and all of its sub-directories:
To find all of the files in the filesystem that were modified in the last 24 hours:
To find all of the files in the web directory and all of its sub-directories that belong to user nginx:
To find all of the files in the working directory whose permissions are 0744:
To find a file with the name aaa in the working directory and list its detailed info:
Conclusion
In this guide, you've gone through the list of the most common Linux commands for everyday use when administering your cloud server. While the commands might seem confusing at first, with time, you'll get used to them once you begin to apply them in a production environment.
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