How to start/stop/restart networking service under Linux operating systems after making changes to IP configuration from a shell prompt ?

Use the following commands as per your Linux distribution to start/stop/restart the networking service.

RedHat / CentOS / Fedora

To start networking service, enter

# /etc/init.d/network start

Or,

# service network start

To stop networking service, enter

# /etc/init.d/network stop

Or,

# service network stop

To restart networking service, enter

# /etc/init.d/network restart

Or,

# service network restart

Ubuntu / Debian

To start networking service, enter

# sudo /etc/init.d/networking start

Or,

# sudo service networking start

To stop networking service, enter

# sudo /etc/init.d/networking stop

Or,

# sudo service networking stop

To restart networking service, enter

# sudo /etc/init.d/networking restart

Or,

# service networking restart

The post How To Restart Networking Service In Linux appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

shutdown command brings the system down in a secure way. All logged-in users are notified that the system is going down, and login is blocked. It is possible to shut the system down immediately or after a specified delay. All processes are first notified that the system is going down by the signal SIGTERM. This gives programs like vi the time to save the file being edited, mail and news processing programs a chance to exit cleanly, etc. shutdown does its job by signalling the init process, asking it to change the runlevel. Runlevel 0 is used to halt the system, runlevel 6 is used to reboot the system, and runlevel 1 is used to put to system into a state where administrative tasks can be performed; this is the default if neither the -h or -r flag is given to shutdown. To see which actions are taken on halt or reboot see the appropriate entries for these runlevels in the file /etc/inittab.(http://linux.about.com/od/commands/l/blcmdl8_shutdow.htm)

Shutdown the machine immediately

Type the following command as root

# shutdown -h now

Shutdown the machine with user defined message

# shutdown -h now 'Server is going down for replace old hardware'

Scheduling the shutdown

Example, schedule shutdown for 3 AM.

# shutdown -h 03:00

Schedule shutdown the system in 5 minutes

# shutdown -h +5

Reboot the machine immediately

# shutdowm -r now

Cancel a running shutdown

# shutdown -c

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Using cron is via the crontab command which allows you to view or edit your crontab file, which is a per-user file containing entries describing commands to execute and the time(s) to execute them.

Display Root cronjob

# crontab -l

Display user cronjob

$ crontab -u user -l

Display daily cronjob

# cd /etc/cron.daily/
# cat * | more

Display hourly cronjob

# cd /etc/cron.hourly/
# cat * | more

Display weekly cronjob

# cd /etc/cron.weekly /
# cat * | more

Display monthly cronjob

# cd /etc/cron.monthly/
# cat * | more

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There are many tools to get hard drive information such as smartctl, hdparm, hwinfo… In this article, i will use hdparm command which provides a command line interface to various hard disk ioctls supported by the stock Linux ATA/IDE device driver subsystem.

hdparm read information such as model number, serial number, device size and much more directly from the drive. Login as root and type the following command

# hdparm -I /dev/sda

Sample output

/dev/sda:

ATA device, with non-removable media
	Model Number:       SAMSUNG HM320HJ                         
	Serial Number:      S2ANJ1MZ804243
	Firmware Revision:  2AK10001
	Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6
Standards:
	Used: unknown (minor revision code 0x0028) 
	Supported: 8 7 6 5 
	Likely used: 8
Configuration:
	Logical		max	current
	cylinders	16383	16383
	heads		16	16
	sectors/track	63	63
	--
	CHS current addressable sectors:   16514064
	LBA    user addressable sectors:  268435455
	LBA48  user addressable sectors:  625142448
	Logical  Sector size:                   512 bytes
	Physical Sector size:                   512 bytes
	device size with M = 1024*1024:      305245 MBytes
	device size with M = 1000*1000:      320072 MBytes (320 GB)
	cache/buffer size  = 16384 KBytes
	Form Factor: 2.5 inch
	Nominal Media Rotation Rate: 7200
Capabilities:
	LBA, IORDY(can be disabled)
	Queue depth: 32
	Standby timer values: spec'd by Standard, no device specific minimum
	R/W multiple sector transfer: Max = 16	Current = 16
	Advanced power management level: 254
	Recommended acoustic management value: 254, current value: 0
	DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
	     Cycle time: min=120ns recommended=120ns
	PIO: pio0 pio1 pio2 pio3 pio4 
	     Cycle time: no flow control=120ns  IORDY flow control=120ns
Commands/features:
	Enabled	Supported:
	   *	SMART feature set
	    	Security Mode feature set
	   *	Power Management feature set
	   *	Write cache
	   *	Look-ahead
	   *	Host Protected Area feature set
	   *	WRITE_BUFFER command
	   *	READ_BUFFER command
	   *	NOP cmd
	   *	DOWNLOAD_MICROCODE
	   *	Advanced Power Management feature set
	    	Power-Up In Standby feature set
	   *	SET_FEATURES required to spinup after power up
	    	SET_MAX security extension
	    	Automatic Acoustic Management feature set
	   *	48-bit Address feature set
	   *	Device Configuration Overlay feature set
	   *	Mandatory FLUSH_CACHE
	   *	FLUSH_CACHE_EXT
	   *	SMART error logging
	   *	SMART self-test
	   *	General Purpose Logging feature set
	   *	64-bit World wide name
	   *	IDLE_IMMEDIATE with UNLOAD
	   *	WRITE_UNCORRECTABLE_EXT command
	   *	{READ,WRITE}_DMA_EXT_GPL commands
	   *	Segmented DOWNLOAD_MICROCODE
	   *	Gen1 signaling speed (1.5Gb/s)
	   *	Gen2 signaling speed (3.0Gb/s)
	   *	Native Command Queueing (NCQ)
	   *	Host-initiated interface power management
	   *	Phy event counters
	   *	Idle-Unload when NCQ is active
	   *	NCQ priority information
	   *	DMA Setup Auto-Activate optimization
	   *	Device-initiated interface power management
	   *	Software settings preservation
	   *	SMART Command Transport (SCT) feature set
	   *	SCT Long Sector Access (AC1)
	   *	SCT LBA Segment Access (AC2)
	   *	SCT Error Recovery Control (AC3)
	   *	SCT Features Control (AC4)
	   *	SCT Data Tables (AC5)
Security: 
	Master password revision code = 65534
		supported
	not	enabled
	not	locked
		frozen
	not	expired: security count
		supported: enhanced erase
	60min for SECURITY ERASE UNIT. 60min for ENHANCED SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 50024e9003dedbf0
	NAA		: 5
	IEEE OUI	: 0024e9
	Unique ID	: 003dedbf0
Checksum: correct

Future reading

hdparm man page
Linux hard disk speed tests

The post How To Find Hard Drive Specifications appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

iptables is a user space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall (implemented as different Netfilter modules) and the chains and rules it stores. Different kernel modules and programs are currently used for different protocols; iptables applies to IPv4, ip6tables to IPv6, arptables to ARP, and ebtables for Ethernet frames.
Iptables requires elevated privileges to operate and must be executed by user root, otherwise it fails to function. On most Linux systems, iptables is installed as /usr/sbin/iptables and documented in its man page,[2] which can be opened using man iptables when installed. It may also be found in /sbin/iptables, but since iptables is not an “essential binary”, but more like a service, the preferred location remains /usr/sbin.
iptables is also commonly used to inclusively refer to the kernel-level components. x_tables is the name of the kernel module carrying the shared code portion used by all four modules that also provides the API used for extensions; subsequently, Xtables is more or less used to refer to the entire firewall (v4,v6,arp,eb) architecture.
Source: http://en.wikipedia.org/wiki/Iptables

In most Linux distros including Redhat / CentOS Linux installs iptables by default. You can use the following procedure to verify that iptables has been installed. Open terminal and type the following command:

root@longvnit:~# iptables -V

Sample outputs:

iptables v1.3.5

You can use the following command to view the status of iptables command, enter:

root@longvnit:~#yum info iptables

Sample outputs:

Installed Packages
Name       : iptables
Arch       : i386
Version    : 1.3.5
Release    : 5.3.el5_4.1
Size       : 552 k
Repo       : installed
Summary    : Tools for managing Linux kernel packet filtering capabilities.
URL        : http://www.netfilter.org/
License    : GPL
Description: The iptables utility controls the network packet filtering code in
           : the Linux kernel. If you need to set up firewalls and/or IP
           : masquerading, you should install this package.

If the above message does not appear, then type the following command to install iptables

root@longvnit:~#yum install iptables

You can use the following command to view rules in all chains:

root@longvnit:~#iptables -L -n

Sample outputs:

Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

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