10 advanced linux command line tools

#10: watch

watch is a beautiful program that executes a program periodically and outputs the contents on a full screen. If you place your command inside quotes, you can even run multiple commands:





watch -n 1 'ls -la ; echo ; vmstat ; echo ; df'

This command executes a file listing, outputs memory statistics and disk space, all separated by empty lines and repeats it every second. How easy is it for you to watch large files gets copied and keep an eye out for disk space issues…

#9: curl

Most (PHP) developers already have met the cURL php extension in their life, but this tool is also available on your command line. Instead of writing an additional php-program just for doing some ‘curly-things’, just use the command line tool. All options you need are available. Just issue “man curl” and find out about all the possibilities.

#8: logsave

logsave is a very nice tool that captures the output of a program and sends it too a log-file. It’s more or less the same what “tee” does, only it will add a begin time stamp and a end time stamp:

jthijssen@guybrush$ logsave -a output.log echo "hello world"
hello world

jthijssen@guybrush$ cat output.log
Log of echo Hello world
Wed Nov 24 16:51:24 2010

Hello world

Wed Nov 24 16:51:24 2010
----------------

The -a parameter will let you append to the log-file.

#7: lsof

lsof stands for “list open files” and displays all the files that your system has currently opened. It’s very useful to figure out which processes uses a certain file, or to display all the files for a single process:

Sample output of "lsof" for a apache httpd process

#6: strace

Strace is one of my favorites. It traces all system calls that a program makes to the linux kernel. This means you can actually “see” when a program opens, closes, reads, write, access files but off course, there are much more calls that you can trace. It’s like running a program without it’s cover.

strace -ff -e trace=open /usr/sbin/apache2

This will strace the program “apache2″ and outputs all the open-calls. Another used version:

strace -ff -p <pid>

traces the currently running process <pid>. This means you don’t have to restart a program to strace it, but you can hook into the currently running system.

One of the main reasons to strace a process is when something is not going right. Either it’s too slow, doesn’t do what you expect it to do or similar. For instance, a program does not read a configuration file you provide. With strace, you can actually trace all the open calls to see if it can find the file, or maybe it just reads a config-file from a different location. It’s a marvelous piece that has saved me hours and hours of debugging.

#5: z* tools

Occasionally you need to grep, diff or cat files that are compressed. Instead of unpacked files, you can easily threat the files as if they were unpacked already by using “zgrep” instead of grep, “zdiff” instead of diff, “zcat” instead of cat etc..

[root@guybrush /]# echo "hello world" | gzip > test.zip
[root@guybrush /]# file test.zip
test.zip: gzip compressed data, from Unix, last modified: Wed Nov 24 17:02:18 2010
[root@guybrush /]# zcat test.zip
hello world

#4: od

It’s not too long ago I discovered this tool myself! It can dump a file into different kind of formats.

[root@guybrush /]# echo "hello world" > test.txt
[root@guybrush /]# od test.txt
0000000 062550 066154 020157 067567 066162 005144
0000014
[root@guybrush /]# od -t xa test.txt
0000000 6c6c6568 6f77206f 0a646c72
          h   e   l   l   o  sp   w   o   r   l   d  nl
0000014
[root@guybrush /]#  od  -t x1u1a test.txt
0000000 68 65 6c 6c 6f 20 77 6f 72 6c 64 0a
        104 101 108 108 111  32 119 111 114 108 100  10
          h   e   l   l   o  sp   w   o   r   l   d  nl
0000014

#3: iconv

iconv is a great tool for all those times you need to convert a file that is encoded one way to convert to another format. For instance, a latin-1 dump of a MySQL database that needs to be imported into another database that is UTF-8 encoded. Iconv can auto-detect the current format. Together with “od” this tool saved my life recently, when somebody mixed up charset encodings so utf-8 multibyte characters were actually encoded AGAIN as utf-8 characters.

#2: nc

netcat (nc) is the tcp/ip swish army knife. It’s capable of almost everything except washing your car and making coffee, although the last one is disputed by some. I use this a lof for checking service requests (like soap-clients) to see if they actually send out the correct headers.

setup a “listening server”:

nc -l 12345

point your soap-client to send data to http://127.0.0.1:12345 and see the data that is being send from your client.

Another common use, but not so much nowadays, since it’s taken over by scp, is data transferring.

Open a listening connection on a client and output all data to a file:

nc -l 12345 > data.dat

on a second server (where your file resides) transfer the data to the client:

nc server-ip:12345 < data.dat

This will transfer the data to the client. As said: using “scp server-ip:data.dat” is probably a much better idea nowadays.

There is much, much more you can do with netcat. Use it in shell scripts to talk to servers (for instance: smtp or http or IRC servers) directly. Again: the manual is your friend.

#1: whiptail

If you install ubuntu, centos, debian, or basically any linux flavor around that doesn’t spawn a graphical shell, you end up in a kind of textual interface . These blueish screen are perfect for quick browsing through installation options. But did you know it’s just as easy for you to use for your own tools?

Examples:

It’s just so easy to create a nice little display box: Just add the text, the height and width and optionally a title.. I’m sure you recognize the interface during installation or kernel upgrades :)

whiptail  --msgbox "Hello world" 5 60 --title "Test dialog" --backtitle "A simple sample.."

A sample messagebox

Ask a user any question. It will return the status code 1 for “no” and status code 0 for “yes”.

whiptail --yesno "Are you sure you want to continue with deployment?" \
10 60 --title "New deployment" --defaultno

A yesno dialog with the default button set to "no"

Menuboxes are similar to html’s select boxes. Add items and let the user choose between them.

whiptail --menu "Please choose the version to deploy" 15 40 5 \
1.0.0-RC1 1 1.0.0-RC2 2 1.0.0-RC3 3

A menu will let a user pick an item quickly

Gauges are a perfect way of letting the user know the status of whatever you are doing. If your program that you will run in the background can output a percentage, whiptail picks that up and displays the correct percentage on the screen. In the example, I use a simple counter from 0 to 100 with a 1/8 second delay. You will see the progress-bar fill up until it reaches 100%.

for i in `seq 0 100` ;  do  echo $i; sleep 0.125; done | \
whiptail --gauge "Deploying..." 10 50 0

It even got gauges!

There are more kind of dialogs you can create with whiptail, read the man pages and find out just how easy it is to make your tools user friendly. Grab all tags from your svn repository with “svn list”, place them in a menu with “whiptail –menu” and make your life just a little easier..

Conclusion

Linux (of better said: unix) philosophy of “do only one thing, and do it good” works. However, this creates a massive forest of tools where even the most experienced users don’t know what each commando does so don’t despair. Know your tools and the job is half done so poke around in the man-pages, /usr/bin and /usr/sbin directories and find out what other gems are still around for you to discover.

MORE COMMANDS:-

System:
Running kernel and system information:

# uname -a # Get the kernel version (and BSD version)
# lsb_release -a # Full release info of any LSB distribution
# cat /etc/debian_version # Get Debian version
Use /etc/DISTR-release with DISTR= lsb (Ubuntu) /etc/issue.
# uptime # Show how long the system has been running + load
# hostname # system's host name
# hostname -i # Display the IP address of the host.
# man hier # Description of the file system hierarchy
# last reboot # Show system reboot history

Hardware Informations:
Kernel detected hardware:

# dmesg # Detected hardware and boot messages
# lsdev # information about installed hardware
# dd if=/dev/mem bs=1k skip=768 count=256 2>/dev/null | strings -n 8 # Read BIOS

# cat /proc/cpuinfo # CPU model
# cat /proc/meminfo # Hardware memory
# grep MemTotal /proc/meminfo # Display the physical memory
# watch -n1 'cat /proc/interrupts' # Watch changeable interrupts continuously
# free -m # Used and free memory (-m for MB)
# cat /proc/devices # Configured devices
# lspci -tv # Show PCI devices
# lsusb -tv # Show USB devices
# lshal # Show a list of all devices with their properties
# dmidecode # Show DMI/SMBIOS: hw info from the BIOS

Load, statistics and messages:
The following commands are useful to find out what is going on on the system.

# top # display and update the top cpu processes
# mpstat 1 # display processors related statistics
# vmstat 2 # display virtual memory statistics
# iostat 2 # display I/O statistics (2 s intervals)
# systat -vmstat 1 # BSD summary of system statistics (1 s intervals)
# systat -tcp 1 # BSD tcp connections (try also -ip)
# systat -netstat 1 # BSD active network connections
# systat -ifstat 1 # BSD network traffic through active interfaces
# systat -iostat 1 # BSD CPU and and disk throughput
# tail -n 500 /var/log/messages # Last 500 kernel/syslog messages
# tail /var/log/warn # System warnings messages see syslog.conf

Users:

# id # Show the active user id with login and group
# last # Show last logins on the system
# who # Show who is logged on the system
# groupadd admin # Add group "admin" and user colin
# useradd -c "Colin Barschel" -g admin -m colin
# usermod -a -G    # Add existing user to group (Debian)
# userdel colin # Delete user colin
# pw groupmod admin -m newmembe r # Add a new member to a group
# pw useradd colin -c "Colin Barschel" -g admin -m -s /bin/tcsh
# pw userdel colin; pw groupdel admin

Kernel modules:

# lsmod # List all modules loaded in the kernel
# modprobe isdn                      # To load a module (here isdn)

Compile Kernel

# cd /usr/src/linux
# make mrproper                      # Clean everything, including config files
# make oldconfig # Reuse the old .config if existent
# make menuconfig # or xconfig (Qt) or gconfig (GTK)
# make # Create a compressed kernel image
# make modules # Compile the modules
# make modules_install # Install the modules
# make install # Install the kernel
# reboot

Repair grub:
So you broke grub? Boot from a live cd, [find your linux partition under /dev and use fdisk to find the linux partion] mount the linux partition, add /proc and /dev and use grub-install /dev/xyz. Suppose linux lies on /dev/sda4:

# mount /dev/sda6 /mnt # mount the linux partition on /mnt
# mount --bind /proc /mnt/proc       # mount the proc subsystem into /mnt
# mount --bind /dev /mnt/dev # mount the devices into /mnt
# chroot /mnt # change root to the linux partition
# grub-install /dev/sda # reinstall grub with your old settings

Listing and PIDs:
Each process has a unique number, the PID. A list of all running process is retrieved with ps.
# ps -auxefw                         # Extensive list of all running process
However more typical usage is with a pipe or with pgrep:

# ps axww | grep cron
586 ?? Is     0:01.48 /usr/sbin/cron -s
# ps axjf # All processes in a tree format
# ps aux | grep 'ss[h]' # Find all ssh pids without the grep pid
# pgrep -l sshd # Find the PIDs of processes by (part of) name
# echo $$ # The PID of your shell
# fuser -va 22/tcp # List processes using port 22 (Linux)
# pmap PID # Memory map of process (hunt memory leaks) (Linux)
# fuser -va /home # List processes accessing the /home partition
# strace df # Trace system calls and signals
# truss df # same as above

Signals/Kill:
Terminate or send a signal with kill or killall.

# kill -s TERM 4712                  # same as kill -15 4712
# killall -1 httpd # Kill HUP processes by exact name
# pkill -9 http # Kill TERM processes by (part of) name
# pkill -TERM -u www # Kill TERM processes owned by www
# fuser -k -TERM -m /home # Kill every process accessing /home (to umount)

Important signals are:
1       HUP (hang up)
2       INT (interrupt)
3       QUIT (quit)
9       KILL (non-catchable, non-ignorable kill)
15     TERM (software termination signal)

Permissions:
Change permission and ownership with chmod and chown. The default umask can be changed for all users in /etc/profile for Linux. The default umask is usually 022. The umask is subtracted from 777, thus umask 022 results in a permission 0f 755.

1 --x execute                        # Mode 764 = exec/read/write | read/write | read
2 -w- write                          # For:       |-- Owner --|   |- Group-|   |Oth|
4 r-- read
ugo=a                              u=user, g=group, o=others, a=everyone
# chmod [OPTION] MODE[,MODE] FILE    # MODE is of the form [ugoa]*([-+=]([rwxXst]))
# chmod 640 /var/log/maillog # Restrict the log -rw-r-----
# chmod u=rw,g=r,o= /var/log/maillog # Same as above
# chmod -R o-r /home/* # Recursive remove other readable for all users
# chmod u+s /path/to/prog # Set SUID bit on executable (know what you do!)
# find / -perm -u+s -print # Find all programs with the SUID bit
# chown user:group /path/to/file # Change the user and group ownership of a file
# chgrp group /path/to/file # Change the group ownership of a file
# chmod 640 `find ./ -type f -print` # Change permissions to 640 for all files
# chmod 751 `find ./ -type d -print` # Change permissions to 751 for all directories

Disk information:

# hdparm -I /dev/sda                 # information about the IDE/ATA disk (Linux)
# fdisk /dev/ad2 # Display and manipulate the partition table
# smartctl -a /dev/ad2 # Display the disk SMART info

System mount points/Disk usage

# mount | column -t # Show mounted file-systems on the system
# df # display free disk space and mounted devices
# cat /proc/partitions # Show all registered partitions

# du -sh * # Directory sizes as listing
# du -csh # Total directory size of the current directory
# du -ks * | sort -n -r              # Sort everything by size in kilobytes

Who has which files opened:
This is useful to find out which file is blocking a partition which has to be unmounted and gives a typical error of:

# umount /home/
umount: unmount of /home             # umount impossible because a file is locking home
   failed: Device busy
# ls -lSr # Show files, biggest last

Find opened files on a mount point with fuser or lsof:

# fuser -m /home                     # List processes accessing /home
# lsof /home

COMMAND   PID    USER   FD   TYPE DEVICE    SIZE     NODE NAME
tcsh    29029 eedcoba cwd    DIR   0,18   12288 1048587 /home/cipi (cipi:/home)
lsof    29140 eedcoba cwd    DIR   0,18   12288 1048587 /home/cipi (cipi:/home)
About an application:

ps ax | grep Xorg | awk '{print $1}'
3324
# lsof -p 3324
COMMAND   PID    USER   FD   TYPE DEVICE    SIZE    NODE NAME
Xorg    3324 root    0w   REG        8,6   56296      12492 /var/log/Xorg.0.log
About a single file:
# lsof /var/log/Xorg.0.log
COMMAND PID USER   FD   TYPE DEVICE SIZE NODE NAME
Xorg    3324 root    0w   REG    8,6 56296 12492 /var/log/Xorg.0.log

Mount/remount a file system
For example the cdrom. If listed in /etc/fstab:

# mount /cdrom
# mount -t auto /dev/cdrom /mnt/cdrom # typical cdrom mount command
# mount /dev/hdc -t iso9660 -r /cdrom # typical IDE
# mount /dev/scd0 -t iso9660 -r /cdrom # typical SCSI cdrom
# mount /dev/sdc0 -t ntfs-3g /windows # typical SCSI
Entry in /etc/fstab:
/dev/cdrom   /media/cdrom subfs noauto,fs=cdfss,ro,procuid,nosuid,nodev,exec 0 0

Add swap on-the-fly
Suppose you need more swap (right now), say a 2GB file /swap2gb .

# dd if=/dev/zero of=/swap2gb bs=1024k count=2000
# mkswap /swap2gb # create the swap area
# swapon /swap2gb # activate the swap. It now in use
# swapoff /swap2gb # when done deactivate the swap
# rm /swap2gb

Mount an SMB share
Suppose we want to access the SMB share myshare on the computer smbserver, the address as typed on a Windows PC is \\smbserver\myshare\. We mount on /mnt/smbshare. Warning> cifs wants an IP or DNS name, not a Windows name.

# smbclient -U user -I 192.168.16.229 -L //smbshare/ # List the shares
# mount -t smbfs -o username=winuser //smbserver/myshare /mnt/smbshare
# mount -t cifs -o username=winuser,password=winpwd //192.168.16.229/myshare /mnt/share
Additionally with the package mount.cifs it is possible to store the credentials in a file, for example /home/user/.smb:
username=winuser
password=winpwd
And mount as follow:
# mount -t cifs -o credentials=/home/user/.smb //192.168.16.229/myshare /mnt/smbshare

Mount an image:

# mount -t iso9660 -o loop file.iso /mnt                # Mount a CD image
# mount -t ext3 -o loop file.img /mnt # Mount an image with ext3 fs

Create a memory file system:
A memory based file system is very fast for heavy IO application. How to create a 64 MB partition mounted on /memdisk:

# mount -t tmpfs -osize=64m tmpfs /memdisk

Disk performance:
Read and write a 1 GB file on partition ad4s3c (/home)

# time dd if=/dev/ad4s3c of=/dev/null bs=1024k count=1000
# time dd if=/dev/zero bs=1024k count=1000 of=/home/1Gb.file
# hdparm -tT /dev/hda      # Linux only

Networking:

# ethtool eth0 # Show the ethernet status (replaces mii-diag)
# ethtool -s eth0 speed 100 duplex full # Force 100Mbit Full duplex
# ethtool -s eth0 autoneg off # Disable auto negotiation
# ethtool -p eth1 # Blink the ethernet led - very useful when supported
# ip link show # Display all interfaces on Linux (similar to ifconfig)
# ip link set eth0 up # Bring device up (or down). Same as "ifconfig eth0 up"
# ip addr show # Display all IP addresses on Linux (similar to ifconfig)
# ip neigh show # Similar to arp -a

Ports in use:
Listening open ports:

# netstat -an | grep LISTEN
# lsof -i # List all Internet connections
# socklist # Display list of open sockets
# netstat -anp --udp --tcp | grep LISTEN
# netstat -tup # List active connections to/from system
# netstat -tupl # List listening ports from system

Firewall
Check if a firewall is running (typical configuration only):

# iptables -L -n -v # For status Open the iptables firewall
# iptables -P INPUT       ACCEPT     # Open everything
# iptables -P FORWARD     ACCEPT
# iptables -P OUTPUT      ACCEPT
# iptables -Z # Zero the packet and byte counters in all chains
# iptables -F # Flush all chains
# iptables -X # Delete all chains

IP Forward for routing
Check and then enable IP forward with :

# cat /proc/sys/net/ipv4/ip_forward # Check IP forward 0=off, 1=on
# echo 1 > /proc/sys/net/ipv4/ip_forward
or edit /etc/sysctl.conf with:
net.ipv4.ip_forward = 1

Network Address Translation

# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE   # to activate NAT
# iptables -t nat -A PREROUTING -p tcp -d 78.31.70.238 --dport 20022 -j DNAT \
--to 192.168.16.44:22           # Port forward 20022 to internal IP port ssh
# iptables -t nat -A PREROUTING -p tcp -d 78.31.70.238 --dport 993:995 -j DNAT \
--to 192.168.16.254:993-995     # Port forward of range 993-995
# ip route flush cache
# iptables -L -t nat            # Check NAT status

DNS
The DNS entries are valid for all interfaces and are stored in /etc/resolv.conf. The domain to which the host belongs is also stored in this file. A minimal configuration is:

nameserver 66.63.128.84
search cipi.net intern.lab
domain cipi.org
Check the system domain name with:
# hostname -d # Same as dnsdomainname

DHCP

# dhcpcd -n eth0           # Trigger a renew (does not always work)
# dhcpcd -k eth0           # release and shutdown
The lease with the full information is stored in:
/var/lib/dhcpcd/dhcpcd-eth0.info

tar
The command tar (tape archive) creates and extracts archives of file and directories. The archive .tar is uncompressed, a compressed archive has the extension .tgz or .tar.gz (zip) or .tbz (bzip2). Do not use absolute path when creating an archive, you probably want to unpack it somewhere else. Some typical commands are:

Create

# cd /
# tar -cf home.tar home/ # archive the whole /home directory (c for create)
# tar -czf home.tgz home/ # same with zip compression
# tar -cjf home.tbz home/       # same with bzip2 compression
Only include one (or two) directories from a tree, but keep the relative structure. For example archive /usr/local/etc and /usr/local/www and the first directory in the archive should be local/.
# tar -C /usr -czf local.tgz local/etc local/www
# tar -C /usr -xzf local.tgz # To untar the local dir into /usr
# cd /usr; tar -xzf local.tgz # Is the same as above

Extract

# tar -tzf home.tgz # look inside the archive without extracting (list)
# tar -xf home.tar # extract the archive here (x for extract)
# tar -xzf home.tgz             # same with zip compression (-xjf for bzip2 compression)
                                # remove leading path gallery2 and extract into gallery
# tar --strip-components 1 -zxvf gallery2.tgz -C gallery/
# tar -xjf home.tbz home/colin/file.txt    # Restore a single file

More advanced

# tar c dir/ | gzip | ssh user@remote 'dd of=dir.tgz' # arch dir/ and store remotely.
# tar cvf - `find . -print` > backup.tar # arch the current directory.
# tar -cf - -C /etc . | tar xpf - -C /backup/etc      # Copy directories
# tar -cf - -C /etc . | ssh user@remote tar xpf - -C /backup/etc      # Remote copy.
# tar -czf home.tgz --exclude '*.o' --exclude 'tmp/' home/

Find

Some important options:
-x (on BSD) -xdev (on Linux)       Stay on the same file system (dev in fstab).
-exec cmd {} \;       Execute the command and replace {} with the full path
-iname       Like -name but is case insensitive
-ls       Display information about the file (like ls -la)
-size n       n is +-n (k M G T P)
-cmin n       File's status was last changed n minutes ago.
# find . -type f ! -perm -444        # Find files not readable by all
# find . -type d ! -perm -111        # Find dirs not accessible by all
# find /home/user/ -cmin 10 -print   # Files created or modified in the last 10 min.
# find . -name '*.[ch]' | xargs grep -E 'expr' # Search 'expr' in this dir and below.
# find / -name "*.core" | xargs rm   # Find core dumps and delete them (also try core.*)
# find / -name "*.core" -print -exec rm {} \; # Other syntax
# Find images and create an archive, iname is not case sensitive. -r for append
# find . $ -iname "*.png" -o -iname "*.jpg" $ -print -exec tar -rf images.tar {} \;
# find . -type f -name "*.txt" ! -name README.txt -print # Exclude README.txt files
# find /var/ -size +10M -exec ls -lh {} \;     # Find large files > 10 MB
# find /var/ -size +10M -ls           # This is simpler
# find . -size +10M -size -50M -print
# find /usr/ports/ -name work -type d -print -exec rm -rf {} \; # Clean the ports
# Find files with SUID; those file are vulnerable and must be kept secure
# find / -type f -user root -perm -4000 -exec ls -l {} \;

Miscellaneous

# which command                      # Show full path name of command
# time command # See how long a command takes to execute
# time cat # Use time as stopwatch. Ctrl-c to stop
# set | grep $USER # List the current environment
# cal -3 # Display a three month calendar
# date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
# date 10022155 # Set date and time
# whatis grep # Display a short info on the command or word
# whereis java # Search path and standard directories for word
# setenv varname value # Set env. variable varname to value (csh/tcsh)
# export varname="value" # set env. variable varname to value (sh/ksh/bash)
# pwd                                # Print working directory
# mkdir -p /path/to/dir # no error if existing, make parent dirs as needed
# mkdir -p project/{bin,src,obj,doc/{html,man,pdf},debug/some/more/dirs}
# rmdir /path/to/dir # Remove directory
# rm -rf /path/to/dir # Remove directory and its content (force)
# rm -- -badchar.txt # Remove file whitch starts with a dash (-)
# cp -la /dir1 /dir2 # Archive and hard link files instead of copy
# cp -lpR /dir1 /dir2 #
# cp unixtoolbox.xhtml{,.bak} # Short way to copy the file with a new extension
# mv /dir1 /dir2 # Rename a directory
# ls -1 # list one file per line
# history | tail -50 # Display the last 50 used commands
# cd - # cd to previous ($OLDPWD) directory

Add/Remove software
Debian/Ubuntu/Mint

# apt-get update                     # First update the package lists
# apt-get install emacs # Install the package emacs
# dpkg --remove emacs # Remove the package emacs
# dpkg -S file # find what package a file belongs to

MORE COMMANDS:-

Procedure for checking System

Check the environment.

...]# set

Show logged in users and what they are doing.

...]# w

Report process status -- make sure all needed processes are running (ex: apache, mysql, ssh).

...]# ps -auxf

Display used/free system memory.

...]# free -m

Display used/free disk memory.

...]# df -h

Display network interface information -- make sure your interfaces are up and running.

...]# ifconfig

Show network connections -- check the ports your system is listening on and the programs behind those ports.

...]# netstat -ape

View logged activity.

...]# less /var/log/secure

View logged activity.

...]# less /var/log/messages

Show listing of last logged in users.

...]# last

Show log of login activity by user name.

...]# lastlog

List loaded modules.

...]# lsmod

Services

chkconfig is a tool for maintaining the /etc/rc[0-6].d directory hierarchy by relieving system administrators of the task of directly manipulating the numerous symbolic links in those directories.

List all of the services which chkconfig knows about.

...]# chkconfig --list

Turn services OFF or ON, under the specified System Run-Levels.

...]# chkconfig --level 0123456 service off/on

Control a Service.

...]# service service-name start/stop/reload

Processes

List running processes with their pids, under a hierarchical structure.

...]# ps -auxf

Kill a process.

...]# kill pid

Really kill a process, if previous kill is unsuccessful.

...]# kill -s 9 pid

Changing Hostname

Edit /etc/sysconfig/network, and re-login into the shell

EditHOSTNAME="www.domain.com"
EditDOMAINNAME="domain.com"

Display new hostname.

...]# hostname

Note that the prompt will now display the host:[user@www dir]#

Update local host aliases

Edit /etc/hosts...

Format is:IP <tab> www.your.domain <tab> alias

For localhost:127.0.0.1 <tab> localhost.localdomain <tab> localhost

Add an extra IP address

...]# cd /etc/sysconfig/network-scripts//etc/sysconfig/network-scripts]# cp ifcfg-eth0 ifcfg-eth0:1

Edit ifcfg-eth0:1...

EditDEVICE="eth0:1"
EditIPADDR="put.extra.ip.here"

Bind IP address.

...]# ifup eth0:1

Put NIC into Promiscuous Mode

Promiscuous mode allows your NIC to read ALL the data that is sent over the wire, and not just the data destined for your IP.

...]# ifconfig eth0 promisc

To remove promiscuous mode...

...]# ifconfig eth0 -promisc

View Process info and Network connections

...]# ps -auxf
...]# netstat -ape
...]# lsof -i

System info

Display Bootup messages:...]# dmesg

Display System information:...]# uname -a

Linux www.domain.com 2.4.20-19.7 #1 Tue Jul 15 13:44:14 EDT 2003 i686 unknown

File Ownership

Change file owner and group:...]# chown owner:group file

Change dir/file owner and group recursively:...]# chown -R owner:group dir

Red Hat Network up2date, command line

Note:

configuration file is located under /etc/sysconfig/rhn/up2date
packages/headers are located under /var/spool/up2date

...]# rhn_register --nox

Change up2date options

...]# up2date --configure

Update the update program

...]# up2date --nox up2date

Show available relevant updated packages

...]# up2date --nox -l

Update system with all relevant packages

...]# up2date --nox -u

Install or Update package

...]#up2date --nox

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Wednesday, September 24, 2014

Simple To Advanced Linux Commands