Linux Config

From: https://linuxconfig.org/linux-configuration-files-top-30-most -important


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Linux Configuration files:
 Top 30 most important

20 February 2023 by Luke Reynolds

Linux is a powerful and flexible operating system, and one of its strengths
is the abundance of configuration files that allow you to customize its
behavior to your needs. In this article, we will be taking a closer look at
some of the most important and widely-used Linux configuration files. From
setting environment variables to managing authentication, these files play a
critical role in ensuring that your Linux system runs smoothly and securely.
Whether you’re a seasoned Linux administrator or just starting out, this
article will provide valuable insights into the inner workings of the Linux
operating system.


In this tutorial you will learn:


An overview of important Linux configuration files
The role of these files in managing various aspects of a Linux system
The functions and responsibilities of files such as /etc/environment,
/etc/default/keyboard, and /etc/security/limits.conf
The significance of files such as /etc/apt/sources.list, /etc/pam.d/system
-auth, and /etc/rsyslog.conf




Linux Configuration files: Top 30 most important


Software Requirements and Linux Command Line Conventions 


Category Requirements, Conventions or Software Version Used
System Any Linux distro
Software N/A
Other Privileged access to your Linux system as root or via the sudo
command.
Conventions # – requires given linux commands to be executed with root
privileges either directly as a root user or by use of sudo command


$ – requires given linux commands to be executed as a regular non
-privileged user

Top 30 most important Linux Configuration files

In this section, we will be presenting a comprehensive list of 30 important
Linux configuration files. The table includes the file name, a brief
description of its purpose, and a few examples of how it can be used to
manage different aspects of a Linux system. Whether you’re looking to
configure the keyboard layout, manage software sources, or ensure that your
log files are properly rotated, this table provides a comprehensive overview
of the most critical Linux configuration files.


File Description
/etc/fstab The /etc/fstab file is used to control the way file systems are
mounted at boot time and during the normal operation of the system. It lists
all available file systems and their mount points, including options and
dump frequencies.
/etc/passwd The /etc/passwd file contains information about the users on
the system, including their username, user ID, group ID, home directory, and
shell. This file is readable by all users on the system, but it is important
to keep it secure to prevent unauthorized access to user accounts.
/etc/shadow The /etc/shadow file contains the encrypted password and other
security information for each user on the system. Unlike /etc/passwd, this
file is only readable by the root user and is therefore much more secure. It
is used to store information such as the last password change, minimum
password age, and maximum password age.
/etc/group The /etc/group file lists the groups on the system and their
members. It contains information about each group, including its name, group
ID, and a list of users who are members of that group. This file is used to
manage user and group permissions for accessing files and directories on the
system.
/etc/sudoers The /etc/sudoers file is used to manage the sudo command,
which allows users to run commands as the root user. This file lists the
users and groups that are allowed to use the sudo command, along with the
commands they are allowed to run. It is important to keep this file secure
to prevent unauthorized access to the root user account.
/etc/ssh/sshd_config The /etc/ssh/sshd_config file is the configuration
file for the SSH server. It specifies options for the server, such as the
port number to listen on, allowed authentication methods, and the location
of host keys. This file is used to secure and configure the SSH server on a
Linux system.
/etc/resolv.conf The /etc/resolv.conf file is used to configure the
system’s DNS resolver. It contains information about the DNS servers that
the system should use for name resolution, as well as search domains and
options. This file is crucial for proper network communication on a Linux
system.
/etc/network/interfaces The /etc/network/interfaces file is used to
configure network interfaces on a Linux system. It contains information
about the network interfaces, such as IP addresses, netmasks, and gateways,
as well as options for configuring DHCP and static IP addresses. This file
is used to manage the network configuration on a Linux system.
/etc/hosts The /etc/hosts file is used to map hostnames to IP addresses.
It is a simple text file that can be used to specify custom hostnames and IP
addresses, bypassing the need to use a DNS server. This file is used to
perform local name resolution on a Linux system.
/etc/sysctl.conf The /etc/sysctl.conf file is used to configure the Linux
kernel parameters at runtime. It contains a list of key-value pairs that can
be used to modify the behavior of the kernel, such as enabling or disabling
IPv4 forwarding, adjusting the maximum number of open file descriptors, and
setting the maximum number of shared memory segments.
/etc/services The /etc/services file lists well-known services and the
port numbers and protocols that they use. It is used by the system to map
service names to port numbers and protocols, making it easier for users to
configure network services. This file is used to manage network services on
a Linux system.
/etc/aliases The /etc/aliases file is used to manage email aliases on a
Linux system. It contains a list of email addresses that are redirected to
other email addresses, allowing users to receive email at multiple addresses
or to redirect email to another address. This file is used to manage email
on a Linux system.
/etc/crontab The /etc/crontab file is the system-wide cron table file. It
is used to schedule tasks to be run automatically by the cron daemon. It
contains a list of commands and the times and dates at which they should be
run. This file is used to automate tasks on a Linux system.
/etc/rc.local The /etc/rc.local file is a script that is run at boot time
by the init process. It contains commands and scripts that should be
executed after the system has finished booting, such as starting services or
setting up environment variables. This file is used to customize the
behavior of a Linux system during boot.
/etc/default/locale The /etc/default/locale file is used to configure the
system locale on a Linux system. It contains information about the default
locale, such as the language, country, and character encoding, that should
be used for system-wide settings. This file is used to manage the locale on
a Linux system.
/etc/environment The /etc/environment file is used to set environment
variables on a Linux system. It contains a list of key-value pairs that are
exported as environment variables, which can be used by applications and
scripts to configure their behavior. This file is used to manage environment
variables on a Linux system.
/etc/default/keyboard The /etc/default/keyboard file is used to configure
the keyboard layout on a Linux system. It contains information about the
keyboard model, layout, variant, and options that should be used for the
system-wide keyboard settings. This file is used to manage the keyboard on a
Linux system.
/etc/security/limits.conf The /etc/security/limits.conf file is used to
set resource limits on a Linux system. It contains a list of key-value pairs
that specify the maximum and minimum values for various system resources,
such as the number of open file descriptors, the size of virtual memory, and
the maximum number of processes. This file is used to manage resource limits
on a Linux system.
/etc/apt/sources.list The /etc/apt/sources.list file is used to configure
the software sources for the APT package manager on a Linux system. It
contains a list of repositories, or software sources, from which packages
can be installed and updated. This file is used to manage software sources
and packages on a Linux system.
/etc/apt/apt.conf The /etc/apt/apt.conf file is used to configure the APT
package manager on a Linux system. It contains a list of options and
preferences that affect the behavior of APT, such as the proxy server to
use, the default release to install packages from, and the default action to
take when upgrading packages. This file is used to manage the APT package
manager on a Linux system.
/etc/bash.bashrc The /etc/bash.bashrc file is the system-wide
configuration file for the bash shell. It contains a list of commands and
settings that are executed whenever a user starts a bash shell session. This
file is used to configure the bash shell for all users on a Linux system.
/etc/sysconfig/network The /etc/sysconfig/network file is used to
configure the network settings on a Linux system. It contains information
about the hostname, gateway, and other network parameters that should be set
when the system starts. This file is used to manage the network settings on
a Linux system.
/etc/modprobe.d/blacklist.conf The /etc/modprobe.d/blacklist.conf file is
used to blacklist modules from being loaded by the Linux kernel. It contains
a list of modules that should not be loaded, either because they are known
to cause problems or because they are not needed on the system. This file is
used to manage the loading of kernel modules on a Linux system.
/etc/udev/rules.d/70-persistent-net.rules The /etc/udev/rules.d/70
-persistent-net.rules file is used to persistently assign network interface
names on a Linux system. It contains a list of rules that match network
interfaces based on their MAC addresses and assigns them stable names, such
as “eth0” or “wlan0”. This file is used to manage the naming of
network interfaces on a Linux system.
/etc/default/grub The /etc/default/grub file is used to configure the GRUB
boot loader on a Linux system. It contains options and settings that affect
the behavior of GRUB, such as the default kernel to boot, the timeout, and
the display resolution. This file is used to manage the GRUB boot loader on
a Linux system.
/etc/X11/xorg.conf The /etc/X11/xorg.conf file is used to configure the X
Window System on a Linux system. It contains information about the graphics
card, monitor, and keyboard, as well as options for customizing the behavior
of the X Window System, such as the color depth and screen resolution. This
file is used to manage the X Window System on a Linux system.
/etc/ld.so.conf The /etc/ld.so.conf file is used to configure the dynamic
linker on a Linux system. It contains a list of directories that should be
searched by the dynamic linker when loading shared libraries. This file is
used to manage the dynamic linker on a Linux system.
/etc/pam.d/system-auth The /etc/pam.d/system-auth file is used to
configure the authentication mechanism on a Linux system. It contains a list
of modules that should be used for authentication, such as checking the
password against the shadow file or using smart cards. This file is used to
manage authentication on a Linux system.
/etc/logrotate.conf The /etc/logrotate.conf file is used to configure the
logrotate utility on a Linux system. It contains information about how log
files should be rotated, such as the frequency, size, and compression of the
rotated logs. This file is used to manage log files on a Linux system.
/etc/rsyslog.conf The /etc/rsyslog.conf file is used to configure the
rsyslog daemon on a Linux system. It contains information about where log
messages should be sent, such as to a remote server or to a local file, as
well as options for filtering and formatting log messages. This file is used
to manage logging on a Linux system.



Conclusion


In conclusion, Linux configuration files play a vital role in ensuring that
your system runs smoothly and securely. From managing environment variables
to configuring the X Window System, these files give you the power to
customize and fine-tune your Linux system to your specific needs. By
understanding the purpose and function of these files, you can gain a deeper
appreciation for the versatility and flexibility of the Linux operating
system. Whether you’re a seasoned Linux administrator or just starting
out, this article provides valuable insights into the world of Linux
configuration files. So if you’re looking to take your Linux skills to the
next level, be sure to familiarize yourself with these important files!

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	N/A
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non -privileged user

File	Description
/etc/fstab	The /etc/fstab file is used to control the way file systems are mounted at boot time and during the normal operation of the system. It lists all available file systems and their mount points, including options and dump frequencies.
/etc/passwd	The /etc/passwd file contains information about the users on the system, including their username, user ID, group ID, home directory, and shell. This file is readable by all users on the system, but it is important to keep it secure to prevent unauthorized access to user accounts.
/etc/shadow	The /etc/shadow file contains the encrypted password and other security information for each user on the system. Unlike /etc/passwd, this file is only readable by the root user and is therefore much more secure. It is used to store information such as the last password change, minimum password age, and maximum password age.
/etc/group	The /etc/group file lists the groups on the system and their members. It contains information about each group, including its name, group ID, and a list of users who are members of that group. This file is used to manage user and group permissions for accessing files and directories on the system.
/etc/sudoers	The /etc/sudoers file is used to manage the sudo command, which allows users to run commands as the root user. This file lists the users and groups that are allowed to use the sudo command, along with the commands they are allowed to run. It is important to keep this file secure to prevent unauthorized access to the root user account.
/etc/ssh/sshd_config	The /etc/ssh/sshd_config file is the configuration file for the SSH server. It specifies options for the server, such as the port number to listen on, allowed authentication methods, and the location of host keys. This file is used to secure and configure the SSH server on a Linux system.
/etc/resolv.conf	The /etc/resolv.conf file is used to configure the system’s DNS resolver. It contains information about the DNS servers that the system should use for name resolution, as well as search domains and options. This file is crucial for proper network communication on a Linux system.
/etc/network/interfaces	The /etc/network/interfaces file is used to configure network interfaces on a Linux system. It contains information about the network interfaces, such as IP addresses, netmasks, and gateways, as well as options for configuring DHCP and static IP addresses. This file is used to manage the network configuration on a Linux system.
/etc/hosts	The /etc/hosts file is used to map hostnames to IP addresses. It is a simple text file that can be used to specify custom hostnames and IP addresses, bypassing the need to use a DNS server. This file is used to perform local name resolution on a Linux system.
/etc/sysctl.conf	The /etc/sysctl.conf file is used to configure the Linux kernel parameters at runtime. It contains a list of key-value pairs that can be used to modify the behavior of the kernel, such as enabling or disabling IPv4 forwarding, adjusting the maximum number of open file descriptors, and setting the maximum number of shared memory segments.
/etc/services	The /etc/services file lists well-known services and the port numbers and protocols that they use. It is used by the system to map service names to port numbers and protocols, making it easier for users to configure network services. This file is used to manage network services on a Linux system.
/etc/aliases	The /etc/aliases file is used to manage email aliases on a Linux system. It contains a list of email addresses that are redirected to other email addresses, allowing users to receive email at multiple addresses or to redirect email to another address. This file is used to manage email on a Linux system.
/etc/crontab	The /etc/crontab file is the system-wide cron table file. It is used to schedule tasks to be run automatically by the cron daemon. It contains a list of commands and the times and dates at which they should be run. This file is used to automate tasks on a Linux system.
/etc/rc.local	The /etc/rc.local file is a script that is run at boot time by the init process. It contains commands and scripts that should be executed after the system has finished booting, such as starting services or setting up environment variables. This file is used to customize the behavior of a Linux system during boot.
/etc/default/locale	The /etc/default/locale file is used to configure the system locale on a Linux system. It contains information about the default locale, such as the language, country, and character encoding, that should be used for system-wide settings. This file is used to manage the locale on a Linux system.
/etc/environment	The /etc/environment file is used to set environment variables on a Linux system. It contains a list of key-value pairs that are exported as environment variables, which can be used by applications and scripts to configure their behavior. This file is used to manage environment variables on a Linux system.
/etc/default/keyboard	The /etc/default/keyboard file is used to configure the keyboard layout on a Linux system. It contains information about the keyboard model, layout, variant, and options that should be used for the system-wide keyboard settings. This file is used to manage the keyboard on a Linux system.
/etc/security/limits.conf	The /etc/security/limits.conf file is used to set resource limits on a Linux system. It contains a list of key-value pairs that specify the maximum and minimum values for various system resources, such as the number of open file descriptors, the size of virtual memory, and the maximum number of processes. This file is used to manage resource limits on a Linux system.
/etc/apt/sources.list	The /etc/apt/sources.list file is used to configure the software sources for the APT package manager on a Linux system. It contains a list of repositories, or software sources, from which packages can be installed and updated. This file is used to manage software sources and packages on a Linux system.
/etc/apt/apt.conf	The /etc/apt/apt.conf file is used to configure the APT package manager on a Linux system. It contains a list of options and preferences that affect the behavior of APT, such as the proxy server to use, the default release to install packages from, and the default action to take when upgrading packages. This file is used to manage the APT package manager on a Linux system.
/etc/bash.bashrc	The /etc/bash.bashrc file is the system-wide configuration file for the bash shell. It contains a list of commands and settings that are executed whenever a user starts a bash shell session. This file is used to configure the bash shell for all users on a Linux system.
/etc/sysconfig/network	The /etc/sysconfig/network file is used to configure the network settings on a Linux system. It contains information about the hostname, gateway, and other network parameters that should be set when the system starts. This file is used to manage the network settings on a Linux system.
/etc/modprobe.d/blacklist.conf	The /etc/modprobe.d/blacklist.conf file is used to blacklist modules from being loaded by the Linux kernel. It contains a list of modules that should not be loaded, either because they are known to cause problems or because they are not needed on the system. This file is used to manage the loading of kernel modules on a Linux system.
/etc/udev/rules.d/70-persistent-net.rules	The /etc/udev/rules.d/70 -persistent-net.rules file is used to persistently assign network interface names on a Linux system. It contains a list of rules that match network interfaces based on their MAC addresses and assigns them stable names, such as “eth0” or “wlan0”. This file is used to manage the naming of network interfaces on a Linux system.
/etc/default/grub	The /etc/default/grub file is used to configure the GRUB boot loader on a Linux system. It contains options and settings that affect the behavior of GRUB, such as the default kernel to boot, the timeout, and the display resolution. This file is used to manage the GRUB boot loader on a Linux system.
/etc/X11/xorg.conf	The /etc/X11/xorg.conf file is used to configure the X Window System on a Linux system. It contains information about the graphics card, monitor, and keyboard, as well as options for customizing the behavior of the X Window System, such as the color depth and screen resolution. This file is used to manage the X Window System on a Linux system.
/etc/ld.so.conf	The /etc/ld.so.conf file is used to configure the dynamic linker on a Linux system. It contains a list of directories that should be searched by the dynamic linker when loading shared libraries. This file is used to manage the dynamic linker on a Linux system.
/etc/pam.d/system-auth	The /etc/pam.d/system-auth file is used to configure the authentication mechanism on a Linux system. It contains a list of modules that should be used for authentication, such as checking the password against the shadow file or using smart cards. This file is used to manage authentication on a Linux system.
/etc/logrotate.conf	The /etc/logrotate.conf file is used to configure the logrotate utility on a Linux system. It contains information about how log files should be rotated, such as the frequency, size, and compression of the rotated logs. This file is used to manage log files on a Linux system.
/etc/rsyslog.conf	The /etc/rsyslog.conf file is used to configure the rsyslog daemon on a Linux system. It contains information about where log messages should be sent, such as to a remote server or to a local file, as well as options for filtering and formatting log messages. This file is used to manage logging on a Linux system.