Many Linux distributions provide a number of tools to simplify network configuration and connectivity verification. The following tools work with every distribution and allow you to administer your network from the command line:
ping: Checks network connectivity
ifconfig: Displays the configuration for a network interface
traceroute: Shows the path taken to reach a host
route: Displays the routing table and/or lets you configure it
arp: Shows the address resolution table and/or lets you configure it
netstat: Displays the status of the network
WORKING IN LINUX WITH THE BASH SHELL
The bash shell serves as the mediator between the user and the Linux kernel, with bash being the most common shell in use today. To interact with the bash shell, you need to understand how the pipe works (allowing the output of one command to be the input of the next), how to use redirection, and some basic commands and environment variables:
Pipe:
command1 | command2
Redirections:
command > file: output goes to file
command < file: input from file
command >> file: append to file
command2> file: errors go to file
Commands:
alias: Defines a shortcut for a long command
apropos: Searches the manpages for keywords
history: Displays the most recent commands
locate: Finds files
whereis: Finds executable files for a command
which: Shows the full pathname for a command
man: Displays online help
printenv: Displays the environment variables
Environment variables:
HOME: User’s home directory
PATH: Directories to search for commands
TERM: Name of a terminal type
LINUX FILE SYSTEM BASICS
To interact with the Linux file system, you must understand some basics: its key directories, some of the most commonly used commands, and the permissions you can assign to files.
Key directories in the file system:
*/: Root directory (base of file system)
/bin: Executable programs
/boot: Linux kernel and boot loader
/dev: Special device files
/etc: System configuration files
/home: Home directories of all users
/lib: Library files for programs
/media: Mount points for CD-ROM and other media
/root: Home directory of the root user
*/sbin: System administration commands
/srv: Data for services such as Web and FTP
*/tmp: Temporary directory
/usr: Many of the important administration programs
/var: Various system files, such as logs
Common commands:
cat: Copies a file to the standard output
cd: Changes the current directory
chmod: Changes file permissions
chown: Changes file ownerships
cp: Copies files
dd: Copies blocks of data
df: Reports disk space usage by device and available space
diff: Compares two text files
du: Reports disk space usage by directory
file: Displays the type of data in a file
find: Finds files based on specified criteria
grep: Searches for text in a file
ln: Links a filename to an alias name
ls: Displays the contents of a directory
mkdir: Creates a directory
more: Displays a text file, one page at a time
mount: Mounts a file system
mv: Renames or moves a file
pwd: Displays the current directory
rm: Deletes files
rmdir: Deletes directories
sort: Sorts lines in a text file
split: Splits a file into smaller parts
umount: Unmounts a file system
wc: Counts the words and lines in a file
File permissions:
rwxrwxrwx: Three sets of rwx. The leftmost set pertains to the owner, the middle set is for the group, and the rightmost set is for others; rwx stands for read (r), write (w), execute (x); the dash (–) means no permission.
rwx——: Only the owner can read, write, and execute.
rw-r–r–: Everyone can read, and the owner can also write.
rw——-: Only the owner can read and write.
r–r–r–: Everyone can read.
Permissions can also be expressed numerically, where read (r) is equal to 4, write (w) is equal to 2, execute (x) is equal to 1, and no permission is equal to 0. Therefore, rwxrwxrwx is equal to 777, rwx—— is equal to 700, rw-r–r— is equal to 644, rw——- is equal to 600, and r–r–r— is equal to 444.