UNIX - Commands - Files, kernel Interact, Env Variables, Work with vi
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19) Managing Files with the shell
cat filename - outputs contents of filename to display
less filename - Allows scrolling while reading contents of filename
mv file1 file2 - Renames file1 to file2
mv file dir-Moves file to specified directory
cp file1 file2 - Copies file1 and creates file2
rm file - Deletes file
rmdir dir - deletes directory(if empty)
grep string files - Searches through files and displays lines containing matching strings
man grep
20) Working with Compressed files
bunzip2 - Expands a compressed file
bzip2 - Compresses or expands files and directories
gunzip - Expands a compressed file
gzip - Compresses or expands files and directories
tar - creates, expands or lists the contents of compressed or uncompressed file or directory archives known as tape archives or tarballs
To create a compressed archive of a directory,use tar’s czf options
tar czf dirname.tgz dirname
To list the contents of the compressed archive, substitute the c option with letter t
tar tzf archive
if many files are in the archive
| tar tzf archive | less |
To expand the contents of a compressed archive, use tar’s zxf options.
21) Use Essential commands from the /bin and /sbin directories
The /bin contains the essential commands used by the system for running and booting linux
/sbin :-In general only the root operator uses the commands in /sbin directory
22) Use and edit files in the /etc directory
fstab - The file system table is a text file listing each hard drive,CD-ROM,floppy or other storage device attached to your PC. Nearly all entries in fstab can be maipulated by root using the mount command.
modprobe.d/-This folder holds all the instructions to load kernel modules that are required as part of the system startup and replaces the historic modprobe.conf file.
passwd :- The list of users for the system, along with user account information.of
shells :- A list of approved shells.
23) Protect the contents of user directories-/home
The most important data on a linux system resides in the user’s directories, found under the /home directory.
24) Use the contents of /proc directory to interact with the kernel
The contents of the /proc directory is created from memory and exists only while Linux is running.
free command obtains its information from a file named meminfo
cat /proc/meminfo
-To turn on kernel protection against one type of denial of service attack known as SYN flooding, use the echo command to send the number 1(one) to the following /proc path.
sudo echo 1>/proc/sys/net/ipv4/tcp_syncookies
getting CPU information, such as family, type and speed from /proc/cpuinfo
viewing important networking information under /proc/net, such as active interfaces information under /proc/net/dev,routing information in /proc/net/route and network statistics in /proc/net/netstat
reporting media mount point information via USB; for example, the linux kernel reports what device to use to access files(such as /dev/sda) if a USB camera or hard drive is detected on the system. You can use the dmesg command to see this information.
24) Work with shared data in the /usr directory
The /usr directory contains software applications, libraries and other types of shared data for use by anyone on the system.
25) Temporary File storage in the /tmp directory.
The /tmp directory is used for temporary file storage
26) Access variable data files in the /var directory
The /var directory contains subdirectories used by various system services for spooling and logging. Many of these variable data files such as print spooler queues, are temporary, whereas others, such as system and kernal loas, are renamed and rotated in use.
27) Using Environment variables
A number of in-memory variables are assigned and loaded by default when the user logs in. These variables are known as shell environment variables, which can be used by various commands to get information about your environment, such as the type of system you are running, your home directory and the shell in use.
PWD :- To provide the name of the current working directory.
USER :- To declare the user’s name, such as andrew.
LANG :- To set language defaults, such as english.
SHELL :- To declare the name and location of the current shell, such as /bin/bash.
PATH :- To set the default location of executable files, such as /bin, /usr/bin and so on.
TERM :- To set the type of terminal in use, such as vt100, which can be important when using screen-oriented programs, such as text editors.
MACHINE :- To declare system type, system architecture and so on.
$env
28) Working with vi
Cursor movement :- h, j, k ,l (left, down, up, right)
Delete character :- x
Delete line :- dd
mode toggle :- Esc, insert(or i)
Quit :- q
Quit without saving :- q!
Run a shell command :- sh (use ‘exit’ to return)
Save file :- w
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