Linux Commands

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

df Disk Free

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

df -h

mount Mount a file system

Mount a file system or device. You can also type mount by itself to show current mounts on the system. Before making the mount, make sure you have a directory on the Linux box to mount the filesystem to. Usually mounts go under the /mnt directory.

Create a mount point

mkdir /mnt/whatever

Once you have the directory set up, you can now mount the filesystem or share.

Linux mounts use nfs usually:

mount -v -t nfs 10.1.1.20:/exportdir /mnt/whatever 

Netware mounts use npc usually:

ncpmount -S [server] -A [IP address] -U [fully distinguished name] -V /vol1 /mnt -o tcp

Example:

ncpmount -S school -A 192.168.100.1 -u admin.wwws  -V vol1 /mnt/nwserver -o tcp

Windows mounts can use cifs or samba:

mount -t cifs //ntserver/download -o username=admin,password=password /mnt/whatever

mount -t smbfs -o username=admin,password=password //ntserver/download /mnt/ntserver

Note: Reload comes with some nice scripts that Tay created for setting up cifs and ncp mounts. They are found under /opt/beginfinite/reload/setup. You just enter the setup information into the corresponding conf file and run the script.

cifsmnt.conf:

1. 1. Author: Tay Kratzer taykratzer@taykratzer.com ##
   2. All values must be kept within double quotes. ##

CIFS_USERNAME="administrator" CIFS_PASSWORD="windoze" CIFS_SHARE="share1" CIFS_SERVERIP="137.65.55.210" CIFS_RETRY_COUNT="10" CIFS_RETRY_SECONDS="30" LINUX_MOUNT_POINT="/mnt/winserver"

ncpmnt.conf:

1. 1. Author: Tay Kratzer taykratzer@taykratzer.com ##
   2. All values must be kept within double quotes. ##

NCP_LOGIN_NAME="admin.acme" NCP_LOGIN_PASSWORD="novell" NCP_VOL="sys" NCPVOL_SERVERIP="137.65.55.210" NCPVOL_SERVERNAME="wwwfs1" NCPVOL_MAP_RETRY_COUNT="10" NCPVOL_MAP_RETRY_SECONDS="30" LINUX_MOUNT_POINT="/mnt/nwserver"

Once you've set up the conf file, run the script from the command line.

umount Unmount filesystem

umount – Unmount a device or mounted filesystem.

testserver:/ # umount /mnt/whatever

Directory Commands

cd Change Directory

Change directory. Tab complete can help traverse the tree.

cd [destination directory]

Change to root directory

cd /

go up one level

cd ..
..

go up two levels

cd ../..
...

du 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

md Create a directory

Creates a directory

md [directory name]
mkdir [directory name]

cp -R Copy a directory

Copy a directory recursively "R"

cp -R "source" "destination"

rm -r 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"

l 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

chmod 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]

Add all the permissions

chmod -R 777 /[destination]

chown 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

cat Concatenate

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 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 }'

Find the number "wc" lines "l" of files "-type f" in a directory structure:

find [directory]/ -type f | wc -l

Report all known instances of a command. A quick way to find out if something is installed.

whereis [commandname]

cp Copy 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]

mv Move file

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

mv -v "file" "destination"

rm Remove or delete a file

Removes a particular file

rm "file"

chmod 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

ln Symbolic link

Make symbolic links between files. This is useful if you need to change the log directory or repair a symbolic link that was removed.

ln -s [path to new directory] ./retain-tomcat7

Network

wget Get File from website

Download the Latest Version of Retain

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

ifconfig

Find the IP address of the server. Use this command to find the IP address(es) and MAC address(es) the system uses. eth0 is the first NIC. If the system has multiple NICs, they are named, eth0, eth1, and so on. lo is loopback.

ifconfig

host

look up mx records

host -t MX [domain.com]

Determine hosts

cat /etc/resolv.conf 

ping

Ping to see if a server is alive. Ctrl-c to stop.

ping [ip address]

DNS

DNS

nslookup
server
dig [servername or ipaddress]

Clear DNS Cache

rcnscd stop 

then

rcnscd start

traceroute

Trace the route to a server

traceroute [domain.com]

hostname

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]

netstat

A useful tool for checking your network configuration and activity.

netstat -lnp -A inet

Process Commands

free Memory usage

Display memory usage

free -m

top System resouces

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

top

vmstat

Report virtual memory statistics: processes, memory, paging, block IO, traps, and cpu activity.

vmstat

chkconfig

Check runlevel of a process

chkconfig [process name]

ps aux Find a process

To find a running process you know the name of

ps aux | grep [process name]

kill End 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]

To kill all processes associated with a particualr name

killall -15 [processname]

w 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

fstab File system information

The fstab file will also contain information about any mounted filesystems as well

cat /etc/fstab

Linux Version

To find the version of Linux that is installed use this command:

cat /etc/*-release

Utilities

history Command history

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]

tar Create archives

Create an uncompressed tape archive of a bunch of files

tar -cvf [dest file name].tar [source directory] 

Extract a tar

tar -xvf [filename] 

zip/gzip Compress files

Zip

zip [dest file name] [source files or directory] 

Unzip

unzip [file].zip -d /[directory]

Create a gzipped tar file

tar -czvf [dest file name] [source directory] 

Extract a gziped tar

tar -xvzf [filename] 

Extract gzip

gzip -dv [file name]

clear Clear Screen

Clear Screen

clear

crontab Schedule Tasks

crontab – Schedule a command to run at a later time.

Each line in the cron (cron is the daemon) table follows the following format: 7 fields left to right. Field Meaning 1 Minute (0-59) 2 Hour (2-24) 3 Day of month (1-31) 4 Month (1-12, Jan, Feb, ...) 5 Day of week (0-6) 0=Sunday, 1=Monday ... or Sun, Mon, Tue, Wed, Thur, Fri 6 User that the command will run as 7 Command to execute

So, if you want to have Netcleanse restart the ntp-client to reset the time every hour, then you'd use this command:

This will load the crontab editor. Add the entry below, save the change and exit the editor.

crontab -e

Restarts ntp-client every minute

0 * * * * root /etc/init.d/ntp-client restart

Runs the script at the top of every hour

00 */1 * * * /root/Desktop/gopostal/gopostalfullauto.sh

date Date and time

This command can be used to display the current time on the server or adjust the time.

date

rpm Package Installer

Package installer. There are numerous useful flags that can be used with this command. For those flags, look here: http://www.novell.com/coolsolutions/tip/19918.html Most commonly, however, you'll just use the commands to install, upgrade and uninstall.

rpm -ivh [filename].rpm

shutdown Shutdown and reboot

Shutdown the server

shutdown -r now
init 6
reboot -f (Last resort reboot method. The only time you'd want to use this option is if something is wrong with the init daemon.)

vi Text Editor

vi – Text editor for Linux. There are a variety of commands you can use in vi, here are some of the most useful:

To open a file:

vi [filename]

• i: Insert text
• ESC: Exit mode, for example, exit the insert text mode
• /: Perform a search (n, repeats search; N, search backwards)
• dd: Deletes a line
• yy: Copies current line
• yw: Copies current word
• u: Undo last change
• p": Pastes whatever was copied after the cursor position

  wq: Writes changes and exits vi

  q!: Quits without saving changes

For more details on using vi, look here: [4]

less Pager program

Less lets you view the contents of a text file by screenfuls.

less [options] [filename]

Options:

• -g: Highlights just the current match of any searched string.
• -I: Case-insensitive searches.
• -M: Shows more detailed prompt, including file position.
• -N: Shows line numbers (useful for source code viewing).
• -S: Disables line wrap ("chop long lines"). Long lines can be seen by side scrolling.
• -?: Shows help.
• +F: Follow mode for log.

Once in less there are a number of commands that you can use:

• spacebar or page down: for next page
• page up or b: for previous page
• enter or j: for next line
• k: for previous line
• Shift-f: for follow mode. ctrl-c to abort follow mode.
• g or <: Return to first line
• G or >: Go to last line
• /[text]: Forward search for [text]
• ?[text]: Backwards search for [text]
• n: Next search match
• N: Previous search match
• ESCu: Turn off match highlighting (see -g option)
• h: Help. q to quit
• q: Quit