Important Files & their Significance in Linux

Directory	Description
/bin	All binaries needed for the boot process and to run the system in single-user mode, including essential commands such as cd, ls, etc.
/boot	Holds files used during the boot process along with the Linux kernel itself
/dev	Contains device files for all hardware devices on the system
/etc	Files used by application subsystems such as mail, the Oracle database, etc.
/etc/init.d	Contains various service startup scripts
/etc/profile.d	Holds application setup scripts run by /etc/profile upon login
/etc/rc.d	Contains subdirectories which contain run level specific scripts
/etc/rc.d/init.d	run level initialization scripts
/etc/rc.d/rc?.d	Where ‘?’ is a number corresponding to the default run level. Contains symbolic links to scripts which are in /etc/rc.d/init.d. For services to be started and stopped at the indicated run level.
/etc/skel	Holds example dot files used to populate a new user’s home directory.
/etc/X11	Contains subdirectories and configuration files for the X Window system
/home	User home directories
/lib	Some shared library directories, files, and links
/mnt	The typical mount point for the user-mountable devices such as floppy drives and CDROM
/proc	Virtual file system that provides system statistics.  It doesn’t contain real files but provides an interface to runtime system information.
/root	Home directory for the root user
/sbin	Commands used by the super user for system administrative functions
/tmp	A standard repository for temporary files created by applications and users.
/usr	Directory contains subdirectories with source code, programs, libraries, documentation, etc.
/usr/bin	Contains commands available to normal users
/usr/bin/X11	X Window system  binaries
/usr/include	Holds include files used in C programs
/usr/share	Contains shared directories for man files, info files, etc.
/usr/lib	Library files searched by the linker when programs are compiled
/usr/local/bin	Common executable application files local to this system
/usr/sbin	Commands used by the super user for system administrative functions
/var	Administrative files such as log files, locks, spool files, and temporary files used by various utilities
/var/www/vhosts/domain1	Contains on my v-server the user directory for a specific domain which is hosted on this serve
/etc/issue	Contains the Ubuntu version you are running. Contains the pre-login message, often overwritten by the /etc/rc.d/rc.local script in Red Hat and some other rpm-based Linux distributions
lsb_release -a	Prints out the Ubuntu version you are running
/etc/apt/source.list	Contains the available sources for software installation
/usr/share/tomcat	Installation directory for tomcat
echo $VARIABLE	Prints the content of the environment variable
sudo /etc/init.d/tomcat5 start/stop	Start / stops the tomcat server
sudo -i	Switches to root
/etc/rsyslog.conf	Log messages  related to system
etc/shadow	Stores Password in encrypted form
/etc/rc.d/rc	Defines which services to start
/var/log/dmesg	Boot time hardware detection and driver setup. Kernel messages taken just after control. kernel  boot messages
/var/log/maillog	Mail System  Messages
/var/log/secure	Security ,authentication & Xinetd messages
/var/log/audit.audit.log	Kernel auditing messages
/var/log/lastlog	Stores information about the last boot process
/var/log/messages	Contains messages produced by the syslog daemon during the boot process.General system messages, includes most of what is in dmesg if it hasn’t “rolled over”. Std. system error messages
/var/log/wtmp	A binary data file holding login time and duration for each user currently on the system
/boot/vmlinuz	The Linux kernel file.  File naming conventions may include release information. The typical location and name of the Linux kernel
/dev/fd0	Device file for the first floppy disk drive on the system
/dev/fd0H1440	Device driver for the first floppy drive in high density mode, commonly invoked when formatting a floppy diskette for that density
/dev/hda	Device file for the first IDE hard drive on the system
/dev/hdc	Commonly, the IDE CDROM drive device file which often is a symbolic link called to /dev/cdrom, the real CDROM driver file.
/dev/null	A dummy device which contains nothing.  It is sometimes useful to send output to this device to make it go away forever. used when you want to send output into oblivion
/etc/crontab	A parent shell script to run commands periodically.  It invokes hourly, daily, weekly, and monthly scripts.
/etc/anacrontab	Runs the job that did not run when the comp. is down
/etc/exports	Contains a list of filesystems which may be made available to other systems on the network via NFS. Specifies hosts to which file systems can be exported using NFS. Man exports contain information on how to set up this file for remote users.
/etc/fstab	The file system table contains the description of what disk devices are available at what mount points. contains information on partitions and file systems used by system to mount different partitions and devices on the directory tree
/etc/mtab	Display the currently mounted system
/etc/group	Holds information regarding security group definitions.
/etc/grub.conf	The grub boot loader configuration file
/etc/hosts	Contains host names and their corresponding IP addresses used for name resolution whenever a DNS server is unavailable
/etc/hosts.allow	Contains a list of hosts allowed to access services on this computer.
/etc/hosts.deny	Contains a list of hosts forbidden to access services on this computer.
/etc/lilo.conf	The lilo boot loader configuration file
/etc/modules.conf	Holds options for configurable system modules
/etc/bashrc	system-wide default functions and aliases for the bash shell
/etc/conf.modules	aliases and options for configurable modules
/etc/DIR_COLORS	Used to store colors for different file types when using ls command. The dircolors command uses this file when there is not a .dir colors file in the user’s home directory. Used in conjunction with the eval command (see below).
/etc/HOSTNAME	Stores the name of the host computer(Used in Debian).For Red Hat Linux it would be /etc/sysconfig/network.
/etc/passwd .	Contains passwords and other information concerning users who are registered to use the system. For obvious security reasons, this is writable only by root and readble by others. It can be modified by root directly, but it is preferable to use a configuration utility such as passwd to make the changes. A corrupt /etc/passwd file can easily render a Linux box unusable.
/etc/resolv.conf	contains a list of domain name servers used by the local machine
/etc/X11/XF86Config	X configuration file. The location in Slackware is /etc/XF86Config.
/proc/cpuinfo	cpu information
/proc/filesystems	prints filesystems currently in use
/proc/interrupts	prints interrupts currently in use
/proc/ioports	contains a list of the i/o addresses used by various devices connected to the computer
/var/log/daemon.log	messages from service tasks like lircd
/var/log/kern.log	if something has gone wrong with a kernel module, you may find something here.
/var/log/Xorg.0.log	start up log from the X server (GUI environment), including hardware detection and modes (resolution) selected
/etc/inittab	Runs different programs and processes on start up. This is typically the program which is responsible for, among other things, setting the default run level, running the rc.sysinit script contained in /etc/rc.d, setting up virtual login terminals, bringing down the system in an orderly fashion in response to [Ctrl][Alt][Del], running the rc script in /etc/rc.d, and running xdm for a graphical login prompt (only if the default run level is set for a graphical login). Describes how the INIT process should set up the system in various runlevels
/etc/securetty	Contains a list of terminals on which root can login. For security reasons, this should not include dialup terminals.
/etc/aliases	File containing aliases used by sendmail and other MTAs (mail transport agents). After updating this file, it is necessary to run the new aliases utility for the changes to be passed to sendmail.
/var/spool/cron	User crontabs are stored here
/etc/sysconfig/selinux	Policy for a system (enforcing ,permissive ,disabled)

Apache Tomcat

File	Description
/usr/share/tomcat5/	Installation directory of Tomcat
psa-webapps	Installation directory for webapps in a vhost environment
/usr/share/tomcat5/conf	Configuration Directory for Tomcat
/etc/default/tomcat5	Contains default settings for tomcat. Most important the used java version (jdk).
/var/log/tomcat5	Log files of tomcat
/etc/init.d/tomcat5 restart	Restart the tomcat webserver

Network

Command	Description
lspci -nn | grep -i net	lspci is a command on Unix-like operating systems that prints ("lists") detailed information about all PCI buses and devices in the system
lsusb	lsusb is a utility for displaying information about USB buses in the system and the devices connected to them
iwconfig	iwconfig is similar to ifconfig, but is dedicated to wireless networking interfaces. It is used to set the parameters of the network interface which are specific to the wireless operation (eg. frequency, SSID)
ifconfig	Shows the network connections
lsmod	lsmod is a command on Linux systems. It shows which loadable kernel modules are currently loaded
python -m SimpleHTTPServer	Start webserver serving current directory tree at http://localhost:8000/

 Some Daily Useful Commands Below:

 Unix

dmidecode -s system-product-name;lspci | grep -i vmware

dos2unix

yum update -x kernel

df -Ph

lsb_release -a

nohup ./script.sh & (continuously run)

stat file or ls -il file for inode

script -a /tmp/filename

ntpq -pn l ntpupdate

rpcinfo -p

ntsysv --level3

modprobe ;lsmod;modinfo

W;tty

ldd (packages dependencies)

rpm2cpio *.rpm |cpio -ivd

rpm -Uvh --rollback '1 hour ago'

rpm -Uvh --rollback 'March 20'

yum history rollback 46

yum history info 46

yum history undo 46

yum history repeat 46

du -h -x --max-depth=2 | egrep "[0-9](M|G)"

du -Th --max-depth=1 /export/data/ndmwbx-vwh114-0/web/jrun4.0

Deleting files in current directory older than 7 days

find . -type f -mtime +7 -print | xargs rm -rf {} \;

Log Rotation

logrotate --force /etc/logrotate.conf

Remotely Force a Reboot:

If you need to remotely hard-reset your Linux system because of a read-only file system, try Magic SysRq:

# echo 1 >/proc/sys/kernel/sysrq ; echo b >/proc/sysrq-trigger

This will enable SYSRQ and power cycle the system, like hitting the reset button. This is obviously a last resort, only when a clean shutdown will not work.

Windows

 

1.wmic os get osarchitecture ; wmic os get Name ;msinfo32

2.wmic os where primary= true call reboot ; shutdown -r -t 10

3.systeminfo |find /I "system type"  

systeminfo | findstr /C:"Total Physical Memory"

4.mstsc /v:0.0.0.0 /f /console ;mstsc /v:0.0.0.0 /f /admin 

5.  Remove dir older than 7 days:

c:\bin\UnixUtils\find -maxdepth 1 -type d -mtime +6 -exec c:\bin\unixutils\rm -rfv {} ;

6.NTP Time Synchronisation

• ^{w32tm /query /configuration}

• ^{w32tm /config /manualpeerlist:ndminf-ntp001 /syncfromflags:manual /reliable:yes /update}

• ^{w32tm /config /update}

• ^{net time /domain /set}

• ^{net stop w32time && net start w32time}

7.Automaticallt RDP using batchscript

cmdkey /generic:"computername or IP" /user:"username" /pass:"password" mstsc /v:"computer name or IP"

8.find out which Domain Controller my PC is talking to

nltest /dsgetdc:domain_name

nltest /dclist:can.edgemcolo.com