The Most Popular Configuration Files in Linux System

List of the most popular configuration files and brief description

Configuration File                  Description

/boot

/boot/grub                             GRUB bootloader file
/boot/grub/menu.list             boot menu
/boot/System.map                 Linux kernel map
/boot/vmlinuz                        Linux kernel

/etc

/etc/apache2/httpd.conf        Apache web server configuration file
                                             (Debian)
/etc/apt/sources.list               lists the sources from which the APT obtains
                                              packages(Debian & Ubuntu)
/etc/at.allow                          users allowed to use the at command to 
                                              schedule jobs
/etc/at.deny                           users forbidden to use the at command
/etc/bashrc                            functions and aliases for bash shell
                                             (Fedora)

/etc/bash.bashrc                    functions and aliases for bash shell
                                             (Debian, SUSE & Ubuntu)
/etc/cups/cupsd.conf            The CPUS scheduler
/etc/fonts/local.conf             font configuration file
/etc/fstab                              Information about the various file system and mount
/etc/group                             Information about groups

/etc/grub.conf                       GRUB bootloader
                                             (Fedora& SUSE)
/etc/hosts                              IP address and their hostnames
/etc/hosts.allow                    Hosts allowed to access internet service
/etc/hosss.deny                     hosts forbidden to access internet services
/etc/httpd/conf/httpd.conf    Apache web server configuration file
                                             (Fedora)

/etc/init.d                              Directory with scripts to start and stop various servers
/etc/init.d/rcS                        Linux initialization script
                                              (Debian, SUSE & Ubuntu)
/etc/inittab                             The init process that starts all the other processes
/etc/issue                               Distribution name and the version number
/etc/lilo.conf                          Linux Loader(LILO) configuration file

/etc/login.defs                       Default information for creating user accounts
/etc/modules.conf                 Configuration file for loadable kernel module
                                             (Debian)
/etc/mtab                               Information about the currently mounted file systems
/etc/passwd                           Information about all user accounts
/etc/profile                            Systemwide environment and startup file for the bash sell

/etc/profile.d                         Directory containing file that the /etc/profile script executes
/etc/rc.d/rc.sysinit                 Linux initialization script
                                              (Fedora)
/etc/shadow                           Secure file with encrypted passwords for all user accounts
/etc/shells                              List of all the shells on the system that the user can use
/etc/skel                                 Directory that holds .bash_logout, .bash_profile, .bashrc files

/etc/sysconfig                        Linux configuration files
                                              (Fedora & SUSE)
/etc/sysctl.conf                      Configuration file with kernel parameters
/etc/termcap                          Database of terminal capabilities and options
                                             (Fedora & SUSE)
/etc/udev                               Directory containing configuration files for udev
/etc/X11                                Directory with configuration files for X Window 
                                              System

/etc/X11/xorg.conf               Configuration file for X.Org X11 the X Window System
                                             (Fedora, Ubuntu & SUSE)
/etc/xinetd.conf                    Configuration for the xinetd daemon that starts internet 
                                             service on demand
/etc/yum.conf                       Configuration for the Yum package updater and installer
                                             (Fedora)

/var

/var/log/apache2                  Web-server access and error logs
                                            (Debian)
/var/log/cron                        Log file with messages from the cron process that runs 
                                            scheduled jobs
/var/log/boot.msg                File with boot messages(SUSE)
/var/log/dmesg                    File with boot messages
                                            (Debian, Fedora & Ubuntu)
/var/log/httpd                      Web-server access and error logs(Fedora)
/var/log/message                 System log


APT    - Advanced Packaging Tool
CPUS - Common Unix Printing System