Difference between revisions of "Linux Commands"

Revision as of 19:40, 23 November 2015

Useful Linux Commands

You can use man [command] to get information about a command, but that is more programmer oriented. You are generally better off going to a search engine and searching for [command] examples.

One of the great powers of Linux is being able to pipe | or redirect outputs from one command to another to do things.

You can also use these commands to create bash scripts.

Disk Commands

Returns a quick overview of what disks are mounted and how full they are in human readable formatting.

df -h

Directory Commands

Directory details

Returns an estimate of file space usage, in human readable format (k,M,G). Warning: May take a long time.

du -h

Returns a total size of the directories under where this command was run and sorts by size.

du -hsx * | sort -rh | head -10

Create a directory

Creates a directory

md [directory name]
mkdir [directory name]

Copy a directory

Copy a directory recursively "R"

cp -R "source" "destination"

Remove a directory

Removes a directory and its contents. Warning: irreversible, fast and dangerous if done in the wrong place with wrong switches. [1]

rm -r "directory"

Directory List

Return a list of files in a directory. This always works (shows file size in bytes)

ls -s

This is a SLES alias of the above

l

Display file size in human-readable values "-h" (K,M,G)

l -h

Sorted by size "S", ascending "r", human-readable "h"

l -Srh

Sorted by time "t", ascending "r", human-readable "h"

l -trh

Show hidden files "a", long list format "l", human-readable "h"

l -alh

Sorted by reverse chonological order l -qaltr

List all open files

lsof

Change Permissions

Permissions are a big deal in Linux [2] not so much in Windows.

Add read and write permissions to User and Group but only read to Other recursively "R" in the destination directory

chmod -R 664 /"destination"

Add Execute, read, and write permissions to User and Group but only read to Other recursively "R" in the destination directory

chmod -R 774 /"destination"

Change Ownership

Ownership of a directory can make a big difference in how Retain works

chown user:group directory/

Change the ownership recursively "R" to user tomcat and group tomcat of the logs directory in the current directory

chown -R tomcat:tomcat logs/

File Commands

Show the contents of a file

cat "filename"

Pipe through more to display a screen full of text at a time (space for next page, enter for next line, ctrl-c to break out)

cat "filename" | more

Pipe through less to display file in less.

cat "filename" | less

Find a file

Find a file from the root of the file system (aka looks everywhere for it) Warning: may take a long time.

find / -name "fileName"

Find all files with the string "log" as part of the filename.

find . | grep log

Find and recursively unzip all items in a directory structure called zippedDir to the current directory.

find /zippedDir -name "*.zip" -exec unzip {} \;

Find files in current directory older than 7 days and delete them.

find . -mtime +7 -exec rm {} \;

Find any file off the root and beyond that is larger than 20M:

find / -type f -size +20M -exec ls -lh {} \; | awk '{ print $NF ": " $5 }'

Copy a file

cp origin /destination/file

To copy particular files recursively

cp -r *.txt /destination

To copy to the current directory

cp /software/origin.file .

To secure copy a file to a remote location

scp [source] [destination IP address]:[username]/[destination]

Sync a file or directory between locations, recurse "r" through subdirectories, retain "a" permissions, ownership and timestamps, verbose "v" logging to screen, show progress "P"

rsync -ravP [source] [destination]

Move a file

Moves file to the destination directory in verbose "v" mode.

mv -v "file" "destination"

Remove or delete a file

Removes a particular file

rm "file"

Change Permissions

Permissions are a big deal in Linux [3] not so much in Windows. Add execute "x" rights to all levels on all shell scripts in the current directory

chmod +x *.sh

Network

Download the Latest Version of Retain

wget "http://download.gwava.com/download.php?product=Retain&version=current"

Find the IP address of the server

ifconfig

look up mx records

host -t MX [domain.com]

Determine hosts

cat /etc/resolv.conf 

DNS

nslookup "Enter"
server "Enter"

Clear DNS Cache

rcnscd stop 

then

rcnscd start

Trace the route to a server

traceroute [domain.com]

Show the system name

hostname

SSH Secure connect to another system, exit to leave ssh shell

ssh [hostname or ip address]

telnet Useful for testing connections. You can send a test email with it:

telnet [IP address or DNS hostname] [port]
ehlo [ENTER]
mail from:  retain@[your domain name]  (note: the "from" can actually be spoofed - it really can contain any text of user@domain.com)[ENTER]
rcpt to: [yours or a user's email address][ENTER]
data[ENTER]
subject:  test email from telnet on Retain server[ENTER]
This is a test[ENTER]
.[ENTER]   (you are literally typing a "period" here and pressing [ENTER])
quit[ENTER]

Process Commands

Display memory usage

free -m

Display an overview of the system resources can be used to find a process

top

Check runlevel of a process

chkconfig [process name]

Find a process

To find a running process you know the name of

ps aux | grep [process name]

Kill a process

You have to find a runaway process with top or ps

kill [process ID]

It the process us hung you may have to be more forceful

kill -9 [process ID]

Who is logged in

Returns a list of logged in users if the TTY column shows "pts/3" that shows us that use is remotely logged in.

who
w

Utilities

Get a history of commands

history

To run a past command

![number of command to run from history]

To run a past command by name

![Ctrl-r][start typing desired command]