Linux Important File Summary

File Directory Description
at.allow, at.deny /etc If at.allow exists, then only the user accounts listed in the file may use the at or batch commands. If at.deny exists, then any user account listed in the file may not use the at or batch commands.
.bash_logout /home/<user> Shell script to clean up any personalized environment settings during logout.
.bash_profile /home/<user> Shell script to set personalized environment settings for each login.
.bashrc /home/<user> Shell script to set personalized functions and aliases for each newly created shell or subshell.
bashrc /etc Shell script to set system-wide functions and aliases. Usually called by /home/<user>/.bashrc.
cron.allow, cron.deny /etc If cron.allow exists, then only the user accounts listed in the file may use the crontab command. If cron.deny exists, then any user account listed in the file may not use the crontab command.
crontab /etc Master cron scheduling file for system-wide jobs. On Red Hat systems, the crontab file uses the run-parts script to schedule any script in the appropriately-named /etc/cron.* directory.
fstab /etc Filesystem declaration and default mount configuration settings.
group /etc List of all user groups on the system and the user membership list for each group.
grub.conf /boot/grub GRUB bootloader configuration settings. Usually linked to from /etc/grub.conf.
inittab /etc init process configuration settings: virtual terminals, default runlevel, runlevel-dependent rc scripts, Ctrl+Alt+Del interrupt handler, X Windows display manager.
lilo.conf /etc LILO bootloader configuration settings.
login.defs /etc Default configuration settings for newly created user accounts and user groups.
logrotate.conf /etc Configuration settings for the cron-scheduled logrotate job. On Red Hat distributions, the logrotate.conf file usually includes other logrotate configuration files from the /etc/logrotate.d directory.
lpd.conf /etc Configuration settings for the lpd print daemon, and defaults for the printcap file.
module-info /boot Kernel Loadable Module definitions and device driver parameters.
modules.conf /etc Configuration files for loading Kernel Loadable Modules during startup. Also known as conf.modules on some Linux distributions.
passwd /etc List of all user accounts on the system. Also includes the user’s UID, GID, full name, home directory, and default shell. Passwords tend to be stored in /etc/shadow on most systems.
printcap /etc Configuration settings for print queues, used by both the lpr command and lpd daemon. Some distributions automatically regenerate this file during startup and use the /etc/printcap.local file to store user customizations.
profile /etc Shell script to set system-wide shell environment settings for all logins.
rc /etc/rc.d Shell script responsible for running the runlevel-dependent shell scripts under the appropriate /rc.d/rcN.d directory, where N is the runlevel.
rc.local /etc/rc.d Last rc shell script run, usually as part of all startup runlevels (1-5). A common location for user-defined startup commands.
rc.sysinit /etc/rc.d Runlevel-independent shell script that mounts filesystems, enables virtual memory swapping, and synchronizes the OS time with the CMOS clock.
services /etc Reference list of common TCP and UDP port numbers and their related services.
shadow /etc Encrypted passwords for all user accounts on the system. Also contains password aging and expiry settings.
syslog.conf /etc Configuration settings for the syslogd and klogd logging daemons.
useradd /etc/default Default configuration settings for newly created user accounts using the useradd command.
XF86Config /etc/X11 Configuration settings for X Windows (XFree86). On some systems, this file may be in the /usr/X11R6/lib/X11 directory.
vmlinuz /boot Compressed Linux kernel image. Usually a symbolic link to the current image file.
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