A summary of the architecture, setup, commands, and administration of a Linux system.
Download the mindmap PDF here:
Get an idea of how a Linux system comes together. Here's a screenshot to show what the PDF looks like.
A list of the base directories in Linux and their purpose, also in the mindmap.
Visually Represented.
## BASE LIBRARIES ##
apt-get -y update
apt-get -y install openssh-server net-tools inetutils-traceroute wireless-tools htop lsof
apt-get -y install yum rpm quota xorg openbox ntpdate ntp postfix mutt cups xinetd cups-bsd rng-tools## DIRECTORIES ##
cat /etc/hostname # Instance's hostname
cat /etc/nsswitch.conf # List of Databases: 'passwd', 'hosts', and sources for those DBs
cat /etc/hosts # Mapping of hostnames to IP addresses
cat /etc/hosts.allow # Allowed hostnames, processed first
cat /etc/hosts.deny # Denied hostnames, processed second
cat /etc/nologin # If exists, only root can login. Contents of file displayed
cat /etc/passwd # DB of info on users, can include hashed passwords, or x
cat /etc/shadow # DB of users and hashed passwords + password config
cat /etc/group # DB of groups + users in groups, can include group passwords
cat /etc/gshadow # DB of groups and hashed passwords + password config
ls /etc/skel # Its contents will be copied to each new user's /home/ directory
cat /etc/profile # Set system wide environmental variables on users shells
file /bin/bash # Unix shell and command language
cat /etc/bash.bashrc # System wide bash initialization file
cat /etc/aliases # Aliases for sendmail. Not bash aliases
cat ~/.profile # User specific shell initialization script/file.
cat ~/.bashrc # Personal bash initialization file for interactive, non-login shells
cat ~/.bash_profile # Personal bash initialization file login shells (console or ssh)
cat ~/.bash_aliases # Personal bash aliases config, can also go bash_profile, or bashrc
cat ~/.bash_login # Additional config executed right after login
cat ~/.bash_logout # Additional config executed right after logout
cat ~/.bash_history # Bash command history
cat /etc/issue # Message or system identification to be printed before the login prompt
cat /etc/os-release # Contains OS info
cat /etc/crontab # Contains the crontab file jobs and scheduling
ls /etc/cron.daily # Contains the crontab scripts to be run daily
cat /etc/anacrontab # Contains the anacrontab file jobs and scheduling
cat /etc/at.allow # Determines which user can submit commands for later execution via at or batch
cat /etc/at.deny # Determines which user can submit commands for later execution via at or batch
cat /etc/protocols # DB of TCP/IP protocols + protocol number + description
cat /etc/services # DB of services and TCP/UDP ports used + description
cat /etc/timezone # Stores configured timezone
cat /etc/localtime # Stores configured localtime
cat /etc/sudoers # Determines the groups and users sudo priviledges. Edit with visudo
ls /etc/sudoers.d/ # Ideal place to add sudoers
cat /etc/ntp.conf # Configuration file for for ntpd
cat /etc/inetd.conf # Configuration file for inetd. Edit requires service restart
cat /etc/xinetd.conf # Configuration file for xinetd. Edit requires service restart
ls /etc/xinetd.d/ # Configuration files for each service managed by xinetd . Edit requires service restart
cat /etc/initramfs-tools/initramfs.conf # Configuration file for initramfs
ls /etc/udev # Device Manager - udev (systemd). Execute changes from kernel in /sys and /dev
cat /etc/udev/udev.conf # udev configuration file.
file /usr/sbin/logrotate # Log rotation utility
cat /etc/logrotate.conf # Configuration file for logrotate
ls /etc/logrotate.d # Configuration files for logrotate - system packages
cat /etc/logrotate.d/rsyslog # Configuration files for logrotate - system rsyslog
cat /etc/rsyslog.conf # Configuration file for syslog
ls /etc/rsyslog.d # Configuration files for services
cat /etc/rsyslog.d/50-default.conf # Default logging rules
cat /etc/updatedb.conf # Config file read by updatedb before updating the locate database
cat /etc/environment # Stores the PATH env variable
cat /etc/fstab # Where should partitions should be mounted and how
ls /etc/rc0.d # System-v runlevel initiation - halt
ls /etc/rc6.d # System-v runlevel initiation - reboot
cat /etc/init/dbus.conf # dbus config file
file /sbin/upstart # Upstart initialization script
ls /etc/init # Contains configuration files used by Upstart
file /sbin/init # System-V initialization script
ls /etc/init.d # Contains scripts used by the System V init tools
cat /etc/init.d/networking # System-v script for service
cat /etc/init.d/cron # System-v script for service
cat /etc/init.d/halt # System-v script for service
cat /etc/init.d/dbus # System-v script for service
cat /etc/init.d/functions # Contains functions to be used by most or all shell scripts stored in the /etc/init.d directory
cat /etc/inittab # describes how the INIT process should set up the system in a certain run-level (RedHat - Sys-V)
ls -lrt /bin/systemd # Systemd initialization script symlink
file /lib/systemd/systemd # Systemd initialization script
ls -lrt /etc/systemd/system/ # Contains symlinks to files in lib/systemd/system/
ls /lib/systemd/system/*.target # Contains init scripts
cat /etc/systemd/journald.conf # Configuration for the systemd journal logging service
cat /etc/default/grub # GRUB config. Run 'update-grub' to update grub.cfg
ls /etc/grub.d/ # Additional files to configure the GRUB menu
cat /boot/grub/menu.lst # GRUB menu list config file
cat /boot/grub/grub.cfg # GRUB 2 menu list config file
cat /etc/dhcp/dhclient.conf # Configuration file for /sbin/dhclient - DHCP
cat /etc/network/interfaces # Network interface configuration information (Debian)
cat /etc/sysconfig/network # Network interface configuration information (RedHat)
cat /etc/sysconfig/network-scripts # Network interface configuration information (RedHat)
cat /etc/ssh/sshd_config # OpenSSH service configuration file
cat /etc/cups/cupsd.conf # Configuration file for the CUPS scheduler
ls /usr/share/X11/xorg.conf.d/ # Xorg configuration file directory
cat /etc/apt/sources.list # Lists the 'sources' from which packages can be obtained
cat /etc/yum.conf # Yum configuration file
ls /etc/yum.repos.d # A list of directories where to look for .repo files
cat /etc/ld.so.conf # Contains a list of directories in which to search for libraries for ldconfig
ls /etc/ld.so.conf.d/ # Directories in which to search for libraries for ldconfig, add new libs here, run ldconfig
ls /lib # Library directory, also searched by ldconfig
ls /usr/lib # Library directory, also searched by ldconfig
ls /dev/sd*# SCSI drives
cat /proc/1/status # Pseudo filesystem with info on running process
cat /proc/1/io # Pseudo filesystem with info on running process
cat /proc/1/syscall # Pseudo filesystem with info on running process
ls /var/log # Main directory for log files
cat /var/log/syslog # Syslog log files
cat /var/log/mail.log # Mail log files - MTA
cat ~/.forward # Email forwarding configuration
ls ~/.ssh/ # Root dir of ssh keys and config
cat ~/.ssh/id_rsa # Example of ssh private key
cat ~/.ssh/id_rsa.pub # Example of ssh public key
cp ~/.ssh/authorized_keys # Configures permanent access using SSH keys - copy .pub keys here
cat /etc/ssh/ssh_known_hosts # Systemwide list of known host keys.
cat ~/.ssh/known_hosts # list of host keys for user not already in the systemwide list## COMMANDS ##
which ls # Locate a command directory
whereis ls # Locate the binary, source, and manual page files for a command
file /etc/passwd # Determine file typetype ls # Display information about command type
who # Show who is logged on
who -r # Print current runlevel
w # Show who is logged on and what they are doing
whoami # Print effective userid
id # Print real and effective user and group IDs
man # An interface to the on-line reference manuals
info # Read Info docum
shutdown # Halt, power-off or reboot the machine
shutdown -c
shutdown -r now
uptime # Tell how long the system has been running.
tzselect # View and adjust timezones
timedatectl # Control the system time and date
timedatectl set-time "2015-11-08 08:00:00"
timedatectl set-timezone "Asia/Kathmandu"
timedatectl set-ntp false
locale # Get locale-specific information - LC_ALL
date # Print or set the system date and time
date +%s # Print or set the system date and time in UNIX epoch time
ntpd # Network Time Protocol (NTP) daemon - auto update
ntpdate # Set the date and time via NTP - manual update
ntpdate pool.ntp.org
hwclock # Read or set the hardware clock (RTC)
hwclock --systohc --localtime
hwclock --systohc --utc
vmstat # Reports information about processes, memory, paging, block IO, traps, disks and cpu activity
lscpu # Display information about the CPU architecture
lspci # List all PCI devices
lsusb # List USB devices
free # Display amount of free and used memory in the system
uname -r # Print system information --kernel-release
uname -p # Print system information --processor
uname -o # Print system information --operating-system
dmesg # Print or control the kernel ring buffer
lsmod # Show the status of modules in the Linux Kernel
modprobe # Add and remove modules from the Linux Kernel
rmmod # Remove a module from the Linux Kernel
env # Display all environment variablesexport# Display all environment variablesexport ENV=/home/user # Create new environment variabledeclare -r ENV=/home/user # Declare variables and give them attributes
crontab -e # Edit crontab for current user
crontab -l # List crontab for current userexport VISUAL=nano; crontab -e # Set nano as default editor
at # Queue jobs for later execution
atq # Examine jobs for later execution
atrm # Delete jobs
batch # Executes commands when system load levels permit
ping # Send ICMP ECHO_REQUEST to network hosts
ping6 # Send ICMP ECHO_REQUEST to network hosts IPv6
dig # DNS lookup utility
nslookup # Query Internet name servers interactively
traceroute # Trace the route to a host
traceroute6 # Trace the route to a host IPv6
tracepath # Traces path to a network host discovering MTU along this path
tracepath6 # Traces path to a network host discovering MTU along this path IPv6
service # Run a System V init script
service --status-all # Display status of all System V managed services
service ssh start # Start System V service
service ssh stop # Stop System V service
service ssh status # Display status of System V service
service ssh restart # Restart System V service
systemctl # Control the systemd system and service manager
systemctl list-units # List known units
systemctl status sound.target # Show terse runtime status information about one or more units
systemctl stop sound.target # Stop (deactivate) one or more units
systemctl start sound.target # Start (activate) one or more units
systemctl enable multi-user.target # Enable one or more unit files or unit file instances
systemctl set-default multi-user.target # Set the default target to boot into.
systemctl set-default graphical.target # Set the default target to boot into.
systemctl isolate multi-user.target # Start the unit specified and stop all others
ifconfig -a # Display all network interfaces, even if down
ifconfig eth0 up # Bring a network interface up
ifconfig eth0 down # Bring a network interface down
ifup # Bring a network interface up
ifdown # Take a network interface down
route # Show / manipulate the IP routing table
route -n # Show numerical addresses instead of trying to determine symbolic host names
route add <> netmask <> gw <># Add a new route with a netmask and a gateway
route del # Delete a route
ip a, ip addr, ip address # Display network interface info
ip link # Display link info
ip route show # Show Routing Table entries
ip route add <>/<> broadcast <> via <> eth0 # Add Routing Table entry
netstat -r # Display the kernel routing tables
netstat -at # Display listening and non-listening sockets
lsof # List open files
lsof /tmp # List open files
iptables -L # List all NAT rules
iwlist ens33 auth # Get wireless information from a wireless interface
netcat -l 12345 # Opens arbitrary TCP and UDP connections and listens
netcat 192.168.0.12 12345 # Sends input to netcat location
nc -l 12345 # Same as netcat
nc 192.168.0.12 12345 # Same as netcat
nmap localhost # Network exploration tool and security / port scanner
dpkg -l # Package manager for Debian - list packages
dpkg -i # Package manager for Debian - install package
dpkg --purge # Purge an installed or removed package, removes everything including conffiles
dpkg-reconfigure # Reconfigure an already installed package
apt-get update # APT package handling utility - update packages from sources in /etc/apt/sources.list
apt-get dist-upgrade # upgrade + attempt to upgrade the most important packages at the expense of less important ones
apt-get install # Install package and dependencies from sources in /etc/apt/sources.list
apt-get remove # Remove package. Leave config files
apt-get purge # Remove package. Delete config files
apt-get autoremove # Remove packages that are no longer needed
apt-cache pkgnames # Prints the name of each package APT knows
apt-cache search # Text search on all available package lists
apt-cache depends # Shows a listing of each dependency a package has
aptitude # Interface to the Debian GNU/Linux package system - APT
rpm -i # RPM Package Manager - install package
rpm2cpio # Extract cpio archive from RPM Package Manager (RPM) package
cpio -idmv # Tool for creating and extracting archives
yum update # Interactive, rpm based, package manager
yum install # Install package and dependencies
yum install --downloadonly --downloaddir=/tmp # Download the package to directory but do not install
yum update # Update packages from sources
yum remove # Remove package
yumdownloader # Download RPM packages from Yum repositories
wget # Utility for non-interactive download of files from the Web
ldconfig # Creates links and cache to shared libraries found in /etc/ld.so.conf, /lib, and /usr/lib
ldconfig -p # Lists of directories and candidate libraries stored in the current cache
ldd /bin/ls # Prints the shared libraries required by the program
ps # Snapshot of the current processes
ps -A # Select all processes
ps -e # Identical to -A
ps aux # See every process on the system using standard syntax
top # Dynamic real-time view of processes running on the system.kill# Send a signal to a process. Default signal for kill is TERMkill -SIGINT 78929
kill -SIGKILL 78929
pkill ping # Send a signal to list of process matching a pattern
killall ping # Kill processes by name
nice -12 large-job # Run a program with modified scheduling priority
renice -5 -p 1575 # Alter priority of running processes
nohup <>&# Run a command immune to hangups, with output to a non-tty. & runs in backgroundbg# Make suspended command to execute in backgroundjobs# List background jobsfg# Bring most recent job to the foregroundfg %1 # Bring a certain job to the foregroundkill %2 # Kill background job
tail -n 5 /var/log/syslog # Output the last 5 lines of file
tail -f /var/log/syslog # Output the last 10 lines of file and continue to display new events
grep # Print lines matching a pattern
grep -E # grep with --extended-regexp
egrep # Same as grep -E
grep -F # grep with --fixed-strings
fgrep # Same as grep -F
rsync # Remote (and local) file-copying toolecho# Display a line of textecho -e # echo + enable interpretation of backslash escapes
./ # Execute the content of the file passed as argument, in the current shellsource# Execute the content of the file passed as argument, in the current shell.# Execute the content of the file passed as argument, in the current shell
chmod # Change permissions for file or folder
chmod +x script.sh # Everyone gets execute permissions
chmod -R 754 myfiledir # Change permissions of folders and files recursively
chown -R daniel:group myfiledir # Change user ownership of folders and files recursively
chgrp -R group myfiledir # Change group ownership of folders and files recursively
useradd # Create a locked new user
useradd -u 1000 -g 500 daniel -G group dans # Create a locked new user in a group
userdel --force --remove daniel # Delete a user
usermod # Modify a user account
usermod -L david # Lock a user's password
passwd # Change a user's password
pwconv # Convert and update user's passwords from passwd to shadow
grpconv # Convert and update groups' passwords from passwd to shadow
groupadd # Create a new group
groupdel # Delete a group
groupmod # Modify a group
gpasswd # Modify a group's password
chage --list daniel # Show account aging information
chage -d 0 daniel # Force immediate password expiration
chage -E "2009-05-31" daniel # Set user password expiry informationumask# Display umask - file permission mask for newly created filesumask -S # Display umask in text
getent hosts # Get entries from Name Service Switch libraries Databases
su = su root # Change user ID or become superuser - overtake session
su daniel # Change user ID or become superuser - overtake session
su - = su - root # Change user ID or become superuser - new session
su - daniel # Change user ID or become superuser - new session
sudo su # Using sudo to invoke su, so to use the sudo password
last # Show a listing of last logged in users
wall # Write a message to all users
visudo # Edit the sudoers fileulimit -a # Show and change all system limitsulimit -u # Show and change system limits for max user processesset# Set or unset values of shell options and positional parametersset -o noclobber # Prevent > from overwrite fileset -x # Print commands and their arguments as they are executedset +x # Disable printing commands and their arguments as they are executed
cat # Concatenate files and print on the standard output
cat -vet # Convert tabs to spaces
expand # Convert tabs to spaces
unexpand # Convert spaces to tabs
wc # Print newline, word, and byte counts for each file
fmt # Reformat each paragraph in the file writing to standard output
pr # Convert text files for printing
join # Join lines of two files on a common field
paste # Write lines from each file side by side, separated by TABs, to standard output
nl # Number lines of files># Redirects output to a file, overwriting the file>># Redirects output to a file appending the redirected output at the end<# Feeds file (right) to command (left). sort < /etc/passwd<<# Feeds file from input until stop character (right) to command (left). sort << END2> # Redirects standard error to file&> # Redirects standard output and standard error to filels /tmp/hello > error.log 2>&1 # Redirects the standard error to the standard output, and both to file2>&1 # Redirects the standard error to the standard outputlogger # Enter messages into the system logtee # Read from standard input and write to standard output and filessort # Sort lines of text filessort -k 3 # Sort lines of text files by fieldsort << END # Sort lines of input string until keyword appearstr -s ' ' < file.txt # Translate or delete characters. Squeeze repeatstr -d 'to_remove' < file.txt # Delete character in set wherever foundsed -e s/Nick/John file.txt # Edit -replace as script inputsed 's/Nick/John/g' file.txtcut -c3 names # Cut character verticallycut -c3-10 names # Cut range of characters verticallycut -d: -f1-2 names # Use delimited to separate into fields, and select specified fieldscut -f 1 -d " " namescut -f 2 -d " " namescut -f 2 -d " " names | paste names -cut -f 2 -d " " names | paste names - | sort -k 3 | cut -f 1uniq # Report or omit repeated linessplit file.txt header_text_for_files # Split a file into piecesiconv -f utf-8 -t ISO_8895-15 < file1.txt > file2.txt # Convert text from one character encoding to anotherxargs # Build and execute command lines from standard inputls name* | xargs pastepwd # Print name of current/working directoryls # List directory contentsls -i # + include inodesls -lrt # + include reverse, long format, time ordering (modification)la # + include hidden . filesalias ls="ls -al" # Create an alias for a compound commandcd # Change directorymv # Move (rename) filescp # Copy files and directoriesrm # Remove files or directoriesscp # Secure copy (remote file copy program)scp -i # + include private keytar -zcvf to.tar.gz files_to_compress # Archiving utility. -z : Compress. -c : Create. -v : Verbose. -f : File to Save.tar -zxvf to.tar.gz files_to_compress # Archiving utility. -z : Decompress. -x : Extract. -v : Verbose. -f : File to Save.tar -cvf to.tar files_to_compress #gzip to.tar >> to.tar.gz # Compress filesgzip -d to.tar.gz >> to.tar # Expand files. -d: decompressfind . -name "protocols" # Search for files in current directory by namefind ./ -name "protocols" # Search for files in current directory by namefind / -name "protocols" # Search for files in / directory by namefind / -inum 129698 # Search for files in / directory by inode numberfind /etc -type f -mtime +30 # Search for files by type and mod time by day-hourfind /etc -type f -size +1M # + add greater than for sizefind /usr -type f -size -1M # + add less than for sizefind /usr -maxdepth 2 -type f -size +1M # + look up to two directies deepfind /var/log -mmin -60 # + last modified n minutes agolocate # Find files/databases by name. Built by updatedbupdatedb # Update a database for mlocate, locate commandln file1 file2 # Make hard link between filesln -s # Make soft link between filesdf # Report file system disk space usagedf -h # + human readable sizesdf -T # + partition typedu # Estimate file space usagedu -h # + human readable sizeslsblk # Info on block devices. Reads the sysfs filesystem and udev dblsblk -f # + filesystemsfdisk /dev/sda # Create disk partition table - MBRfdisk -l /dev/sda # List disk partition table - MBRgdisk /dev/sda # Create GUID partition table (GPT)gdisk -l /dev/sda # List GUID partition table (GPT)parted # Create GUID partition table (GPT)mkfs /dev/sdb1 # Build a Linux filesystem on a hard disk partitionmkfs -t ext3 /dev/sdb1 # + filesystem typemkfs.ext3 /dev/sdb1 # + dot notation. Recommended way to call mkfsmkfs.xfs -f /dev/sdb1 # + force overwritemount /dev/sdb1 /mnt/Photos # Mount a filesystem to the file treeumount /mnt/Photos # Unmount a filesystemmkswap /dev/sdb2 # Sets up a Linux swap area on a device or in a fileswapon /dev/sdb2 # Enable/disable devices and files for paging and swappingswapoff /dev/sdb2 # Enable/disable devices and files for paging and swappingfsck /dev/sda1 # Check and repair a Linux filesysteme2fsck /dev/sda1 # Check and repair a Linux ext2/ext3/ext4 file systemdumpe2fs -h /dev/sda1 # Dump ext2/ext3/ext4 filesystem information + only display the superblock infotune2fs -l /dev/sda1 # List the contents of the filesystem superblocktune2fs -L Photos /dev/sda1 # Set the volume label of the filesystemtune2fs -c 10 /dev/sda1 # Adjust the number of mounts after which the filesystem will be checked by e2fsckfuser /tmp # Identify processes using files or sockets/etc/fstab # To configure quotas, edit and add usrquota and grpquota to filesystem, rebootquotacheck -avug # Initial quota check on filesystem. Create a aquota file for user and groupquota -u daniel testuser # Display disk usage and limits for userquota -g group testuser # Display disk usage and limits for groupedquota -u daniel # Edit user quotasedquota -g group # Edit group quotasrepquota /mnt/Photos # Display disc usage and quotas for a filesystemquotaon /mnt/Photos # Enable filesystem quotasquotaoff /mnt/Photos # Disable filesystem quotasdd if=/dev/sda of=bootloader.bak bs=446 count=1 # Copy and convert file. if - input file, of = output file, bs - bytesxxd bootloader.bak # Make a hexdump or do the reverseod # Dump files in octal and other formatsgrub-probe --version # Probe device information for GRUBgrub-probe --target=fs /boot/grub #grub-probe --target=drive --device /dev/sda #grub-install /dev/sda # Install GRUB to a devicegrub-mkconfig -o /boot/grub/grub.cfg # Generate a GRUB configuration fileupdate-grub # Same as: grub-mkconfig -o /boot/grub/grub.cfginit 3 # Change systemd runlevel to 3telinit 3 # Change SysV runlevel to 3screen -ls # List available screensscreen -r 1499.screen_name # Reattach to a particular screen idscreen # Create a new screen session with a default idscreen -S screen_name # Create a new screen session - Press CTRL-A + d to detachapt-get -y install xorg # Install X11 - X Server Window systemstartx # Initialize an X sessionapt-get -y install openbox # Install Extensible Window Managerstartx # Initialize an X session with a Window Managerapt-get -y install lightdm gnome # Install Display Managersexport DISPLAY=:1 # Export displays for us to connect toxterm # Open another terminalxwininfo # Get info about my screenxdpyinfo # Get technical info about x serverxhost + # Allow anyone to connect to serverxhost - # Allow only authorised clients to connect to serverjournalctl -b -1 # Query the systemd journal - Show messages from a specific bootjournalctl --since "2 days ago" # Show messages from 2 days agomutt # Text based program for reading and sending emailmail -s "Hello World" someone@example.commail -s "This is the subject" somebody@example.com <<< 'This is the message'mailq # List the mail queuenewaliases # Initialize the alias databaselpq # Show printer queue statuslpc # Cancel Printer Joblpr # Print filecupsenable printer_name # Stop/start printers and classescupsdisable printer_name # Stop/start printers and classesssh-keygen # Generates, manages and converts authentication keys for sshchmod 700 ~/.ssh/ # Permissions best practices for ssh keyschmod 644 ~/.ssh/id_rsa.pub # Permissions best practices for ssh keyschmod 600 ~/.ssh/id_rsa # Permissions best practices for ssh keyseval `ssh-agent` # ssh-agent is a background program that handles passwords for SSH private keysssh-add # Prompts the user for a private key password and adds it to the list maintained by ssh-agenttouch file1.txt # Creates filerngd -r /dev/urandom # Creates some entropy to be able to use gpggpg --gen-key # Generate a new key pair using the current default parametersgpg --gen-revoke your_email@address.com # Generate a revocation certificate for the complete keygpg --keyserver pgp.mit.edu --search-keys params # Set a preferred keyserver for the specified user ID, search for keygpg --list-keys # List all keys from the public keyringsgpg --encrypt --recipient user file1.txt # Encrypt datala -la text1.txt.gpggpg --decrypt file1.txt.gpg > file1.txt # Decrypt data## ENV VARIABLES ##
LD_LIBRARY_PATH # LD_LIBRARY_PATH is an environment variable you set to give the run-time shared library loader (ld.so)# an extra set of directories to look for when searching for shared libraries.# This list is prepended to the existing list of compiled-in loader paths for a given executable, and any system default loader paths.# For security reasons, LD_LIBRARY_PATH is ignored at runtime for executables that have their setuid or setgid bit set.# This severely limits the usefulness of LD_LIBRARY_PATH.
HOME # Contains the path to the home directory of the current user
PATH # Contains a colon-separated list of directories in which your system looks for executable files## SCRIPTING ###!/bin/bashif [ -f"$1" ]
thenecho"$1 is a file"elseecho"$1 is not a file"fiif [ "$1"="cool" ]
thenecho"Cool Beans"elif [ "$1"="neat" ]
fiif [ "$#"-gt 0 ]
thenecho"There's Beans"fiforindexin 1 2 3 4 5
doecho$indexdoneforiin$(seq 1 100)doecho$idoneecho"Please enter your name"read name
echo"Hello, $name. How are you?"
i = 0
while i != 10
do
i = `expr i + 1`doneechoFunction() {
echo"echo is Called"
}
echoFunction;echo$?