If you use Memcached server to store application data, you may want to invalidate it once you deploy a new version to avoid corruption or weird results… In this article, I’ll show you How do I flush the entire contents of a Memcached server ?

Using telnet command

I often use telnet to flush the entire contents of Memcached server, type the following command

# telnet localhost 11211

Output

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
flush_all
OK
quit
Connection to localhost closed by foreign host.

Where
– localhost: Memcached server instance
– 11211: Memcached server port

Using netcat command

# echo "flush_all" | nc localhost 11211

By default, nc (or netcat) creates a TCP socket either in listening mode (server socket) or a socket that is used in order to connect to a server (client mode). Actually, netcat does not care whether the socket is meant to be a server or a client. All it does is to take the data from stdin and transfer it to the other end across the network.

Restart Memcached Server

Login as root and type the following command

# /etc/init.d/memcached restart

Restarting your application is not ideal however, you will lose anything cached in memory, cause delays to users trying to access your site, that sort of thing.

Using PHP script

Create php file with the following content

# vi flush_memcached.php
$memcache = new Memcache;
$memcache->connect('localhost', 11211);
$memcache->flush();

To execute this script, type the following command

# php flush_memcached.php

The post How To Flush The Entire Contents Of Memcache Server appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

A master boot record (MBR) is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk. MBRs are usually placed on storage devices intended for use with IBM PC-compatible systems.

MBR Total Size

446 + 64 + 2 = 512

Where,
446 bytes – Bootstrap.
64 bytes – Partition table.
2 bytes – Signature.

Backup MBR

Linux or Unix provides “dd” tool to backup any file. Usually, you must be “root” so that you can use it.

# dd if=/dev/sda of=/backup/mbr_sda.bak bs=512 count=1

Above command will copy 512 bytes (MBR) from sda to mbr_sda.bak

Restore MBR

To restore the MBR and partition table, type the following command

# dd if=/backup/mbr_sda.bak of=/dev/hda bs=512 count=1

To restore the MBR, type the following command

# dd if=/backup/mbr_sda.bak of=/dev/hda bs=446 count=1

The post How To Backup & Restore Master Boot Record (MBR) In Linux appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

RAR stands for Roshal ARchive. It is a proprietary archive file format that supports data compression, error recovery, and file spanning. It was developed by a Russian software engineer, Eugene Roshal (the first letter of his surname contributing to the name of the archive format), and is currently licensed by win.rar GmbH.

The filename extension used by RAR is .rar for the data volume set and .rev for the recovery volume set. In previous versions, if a RAR-archive was broken into many smaller files (a “multi-volume archive”), then the smaller files used the extensions .rar, .r00, .r01, .r02 etc.

Install unrar command

To extract RAR files under Linux system, you need to install unrar command. There are some ways to install unrar command. Under Ubuntu/Debian Linux, type the following command

# apt-get install unrar

If you are using Fedora core Linux then type the following command

# yum install unrar

If any of above, methods is not working, download binary package from official rarlab site, enter

# wget http://www.rarlab.com/rar/rarlinux-4.0.1b1.tar.gz

To Extract rarlinux-4.0.1b1.tar.gz, type the following command

# tar zxvf rarlinux-4.0.1b1.tar.gz

Sample output

rar/
rar/readme.txt
rar/default.sfx
rar/whatsnew.txt
rar/license.txt
rar/order.htm
rar/rar
rar/unrar
rar/rar_static
rar/technote.txt
rar/rarfiles.lst
rar/makefile
rar/rar.txt

Now copy rar and unrar commands to /bin directory, type the following command

# cd rar
# cp rar unrar /bin

How to use unrar

To extract rar file in current directory, type the following command

$ unrar e file.rar

To list file inside rar archive, type the following command

$ unrar l file.rar

To extract file with full path, type the following command

$ unrar x file.rar

To test integrity of archive file, type the following command

$ unrar t file.rar

The post How To Extract RAR Files Under Linux appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

If you store private information on your Linux system and you want to prevent other people who use the system from viewing your private files, you need to password protect these files. Solution is to use following commands to encrypt or decrypt files with a password.

gpg command

GnuPG is the GNU project’s complete and free implementation of the OpenPGP standard as defined by RFC4880. GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications.

To encrypt a file, use command gpg as follows:

$ gpg -c filename

Example, to encrypt private.txt file, type the command

$ gpg -c private.txt

Output

Enter passphrase:
Repeat passphrase:

Where,
-c : Encrypt with symmetric cipher.

To decrypt file use gpg command

$ gpg private.txt.gpg

Output:

gpg private.txt.gpg
gpg: CAST5 encrypted data
Enter passphrase:

mcrypt command

Mcrypt is a simple crypting program, a replacement for the old unix crypt. When encrypting or decrypting a file, a new file is created with the extension .nc and mode 0600. The new file keeps the modification date of the original. The original file may be deleted by specifying the -u parameter.

Examples, to encrypt data.txt file, type the following command

$ mcrypt data.txt

Output:

Enter the passphrase (maximum of 512 characters)
Please use a combination of upper and lower case letters and numbers.
Enter passphrase:
Enter passphrase:

Note that a new file is created with the extension .nc.

To decrypt the data.txt.nc file, enter

$ mcrypt -d data.txt.nc

Output:

Enter passphrase:
File data.txt.nc was decrypted.

The post Linux Password Protect Files appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

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.

The lsof command or “list open files” command in Linux is a powerful tool. In Linux and Unix everything behind the scenes are just files. This includes IP sockets, pipes, unix sockets, directories, devices, even inodes are just files. This means that lsof can actually tell you a lot of information of what is going on on your system.

Synopsis

lsof [ -?abChlnNOPRstUvVX ] [ -A A ] [ -c c ] [ +|-d d ] [ +|-D D ] [ +|-f [cfgGn] ] [ -F [f] ] [ -g [s] ] [ -i [i] ] [ -k k ] [ +|-L [l] ] [ -m m ] [ +|-M ] [ -o [o] ] [ -p s ] [ +|-r [t] ] [ -S [t] ] [ -T [t] ] [ -u s ] [ +|-w ] [ -- ] [names] 

Example 1: Show all opened files

Type the following command

lsof | more

Sample outputs

COMMAND     PID      USER   FD      TYPE     DEVICE      SIZE       NODE NAME
init          1      root  cwd       DIR      253,4      4096          2 /
init          1      root  rtd       DIR      253,4      4096          2 /
init          1      root  txt       REG      253,4     38652   41746599 /sbin/init
init          1      root  mem       REG      253,4    129900   16252964 /lib/ld-2.5.so
init          1      root  mem       REG      253,4   1693812   16252965 /lib/libc-2.5.so
init          1      root  mem       REG      253,4     20668   16253168 /lib/libdl-2.5.so
init          1      root  mem       REG      253,4    245376   16253222 /lib/libsepol.so.1
init          1      root  mem       REG      253,4     93508   16253815 /lib/libselinux.so.1
init          1      root   10u     FIFO       0,17                 1277 /dev/initctl
...

Example 2: Show all opened internet sockets

Using the -i flag lsof will list the internet sockets currently opened

lsof -i

Sample outputs

COMMAND     PID   USER   FD   TYPE   DEVICE SIZE NODE NAME
sshd       2537   root    3u  IPv6     5348       TCP *:rockwell-csp2 (LISTEN)
mysqld     2625  mysql   11u  IPv4     5463       TCP *:mysql (LISTEN)
httpd      2731 apache    3u  IPv6 30048993       TCP *:http (LISTEN)
...

Example 3: Shows all networking related to a given port 80

lsof -i :80

Sample outputs

COMMAND   PID   USER   FD   TYPE   DEVICE SIZE NODE NAME
httpd    2731 apache    3u  IPv6 30048993       TCP *:http (LISTEN)
httpd    2731 apache   58u  IPv6 39448263       TCP server.com:http->adsl-dynamic-pool-xxx.hcm.fpt.vn:23527 (ESTABLISHED)
httpd    2731 apache   60u  IPv6 39448302       TCP server.com:http->crawl-66-249-69-83.googlebot.com:35190 (ESTABLISHED)
httpd    2731 apache   61u  IPv6 39448336       TCP server.com:http->v16-13.opera-mini.net:37548 (ESTABLISHED)
httpd    2731 apache   62u  IPv6 39448388       TCP server.com:http->v16-13.opera-mini.net:37561 (ESTABLISHED)
httpd    2731 apache   64u  IPv6 39447543       TCP server.com:http->adsl.viettel.vn:13636 (FIN_WAIT2)

Example 4: Show all TCP/UDP connections

lsof -i TCP

Sample outputs

sshd       2537   root    3u  IPv6     5348       TCP *:rockwell-csp2 (LISTEN)
mysqld     2625  mysql   11u  IPv4     5463       TCP *:mysql (LISTEN)
httpd      2731 apache    3u  IPv6 30048993       TCP *:http (LISTEN)
...

Example 5: List open files associated with process ID

The flag +p will display all open files associated with specific process ID, example with process ID is 2625

lsof +p 2625

Sample outputs

COMMAND  PID  USER   FD   TYPE     DEVICE      SIZE     NODE NAME
mysqld  2625 mysql  cwd    DIR      253,4      4096 21495811 /var/lib/mysql
mysqld  2625 mysql  rtd    DIR      253,4      4096        2 /
mysqld  2625 mysql  txt    REG      253,4   7020300 50999198 /usr/libexec/mysqld
mysqld  2625 mysql  DEL    REG      253,4           16253135 /lib/libcrypto.so.0.9.8e.#prelink#.64u8kX
mysqld  2625 mysql  mem    REG      253,4           16252984 /lib/libm-2.5.so (path inode=16253122)
mysqld  2625 mysql  DEL    REG      253,4           50996047 /usr/lib/libgssapi_krb5.so.2.2.#prelink#.YYIHuy
mysqld  2625 mysql  mem    REG      253,4           16252990 /lib/libselinux.so.1 (path inode=16253815)
mysqld  2625 mysql  mem    REG      253,4           16256252 /lib/libsepol.so.1 (path inode=16253222)
mysqld  2625 mysql  mem    REG      253,4     50848 16253138 /lib/libnss_files-2.5.so
mysqld  2625 mysql  mem    REG      253,4           16253825 /lib/librt-2.5.so (path inode=16253220)
mysqld  2625 mysql  mem    REG      253,4           16252942 /lib/ld-2.5.so (path inode=16252964)
mysqld  2625 mysql  mem    REG      253,4           50996107 /usr/lib/libstdc++.so.6.0.8 (path inode=50989584)
mysqld  2625 mysql  mem    REG      253,4           50996061 /usr/lib/libkrb5.so.3.3 (path inode=50999803)
mysqld  2625 mysql  mem    REG      253,4           16252980 /lib/libdl-2.5.so (path inode=16253168)
...

Example 6: Show what a given user has open

The flag -u will show what a given user has open

lsof -u apache

Sample outputs

COMMAND   PID   USER   FD   TYPE     DEVICE      SIZE     NODE NAME
httpd    2731 apache  cwd    DIR      253,4      4096        2 /
httpd    2731 apache  rtd    DIR      253,4      4096        2 /
httpd    2731 apache  txt    REG      253,4   3120954 51157630 /usr/local/apache/bin/httpd
httpd    2731 apache  mem    REG      253,4    375710 51157607 /usr/local/apache/lib/libaprutil-1.so.0.3.10
httpd    2731 apache  mem    REG      253,4     45432 16253184 /lib/libcrypt-2.5.so
httpd    2731 apache  mem    REG      253,4      7748 16253849 /lib/libcom_err.so.2.1
httpd    2731 apache  mem    REG      253,4      7880 16253845 /lib/libkeyutils-1.2.so
httpd    2731 apache  mem    REG      253,4    937178 51157689 /usr/local/apache/modules/mod_security2.so
httpd    2731 apache  mem    REG      253,4    129208 16253851 /lib/libpcre.so.0.0.1
...

The post 10 lsof Command Examples appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

What is Monit ?

Monit is a free open source utility for managing and monitoring, processes, files, directories and filesystems on a UNIX system. Monit conducts automatic maintenance and repair and can execute meaningful causal actions in error situations.

What Monit can do

Monit can start a process if it does not run, restart a process if it does not respond and stop a process if it uses too much resources. You can use Monit to monitor files, directories and filesystems for changes, such as timestamp changes, checksum changes or size changes. You can also monitor remote hosts; Monit can ping a remote host and can check TCP/IP port connections and server protocols. Monit is controlled via an easy to use control file based on a free-format, token-oriented syntax. Monit logs to syslog or to its own log file and notifies you about error conditions and recovery status via customizable alert.

Install Monit

The first, you need to enable EPEL (Extra Packages for Enterprise Linux) to install monit package. Login as root and type the following command:

[root@lifelinux ~]# vi /etc/yum.repos.d/epel.repo

Add or uncomment the following content at end of the file

[epel]
name=Extra Packages for Enterprise Linux 5 - $basearch
mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=epel-5&arch=$basearch
failovermethod=priority
enabled=1
gpgcheck=0

Save and close the file. And type the following command

[root@lifelinux ~]# yum clean all

To install monit, type the following command

[root@lifelinux ~]# yum install monit

Turn on monit when system start up

[root@lifelinux ~]# chkconfig --levels 235 monit on

Configure Monit

The configuration file of monit in Centos or RedHat is /etc/monit.conf. Type the following command to edit

[root@lifelinux ~]# vi /etc/monit.conf

Sampe configuration file

set daemon 60
set logfile /var/log/monit.log
set mailserver localhost
set mail-format { from: alert@domain.com
subject: $SERVICE $EVENT at $DATE
message: Monit $ACTION $SERVICE at $DATE on $HOST: $DESCRIPTION.
}
set alert admin@domain.com
include /etc/monit.d/*

Now to monitor Apache, create a file /etc/monit.d/httpd, enter

[root@lifelinux ~]# vi /etc/monit.d/httpd

Add following content

check process httpd with pidfile /var/run/httpd.pid
group apache
start program = "/etc/init.d/httpd start"
stop program = "/etc/init.d/httpd stop"
if failed host 127.0.0.1 port 80
protocol http then restart
if 5 restarts within 5 cycles then timeout

MySQL server restart configuration directives

check process mysqld with pidfile /var/run/mysqld/mysqld.pid
group mysql
start program = "/etc/init.d/mysqld start"
stop program = "/etc/init.d/mysqld stop"
if failed host 127.0.0.1 port 3306 then restart
if 5 restarts within 5 cycles then timeout

SSH server configuration directives

check process sshd with pidfile /var/run/sshd.pid
start program "/etc/init.d/sshd start"
stop program "/etc/init.d/sshd stop"
if failed host 127.0.0.1 port 22 protocol ssh then restart
if 5 restarts within 5 cycles then timeout

Type the following command to start monit

[root@lifelinux ~]# /etc/init.d/monit start

You can verify that monit is started from /var/log/monit.log log file:

[root@lifelinux ~]# tail -f /var/log/monit.log

Sample ouputs

[ICT May 12 14:51:18] info     : 'system_server2.domain.com' Monit started

Further readings

Monit home page
Monit documenation
Monit configuration examples

The post How To Install Monit On Centos / Redhat appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

If you want to SSH login without password or automate your task between two servers, you need to setup SSH login via certificate.

This topic has detail steps on How to setup an SSH cetificate.

Step1: Generating RSA key

You login to your server and type the following command:

[root@lifelinux~]#ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
a5:4c:29:3f:92:be:ee:41:03:8d:aa:59:c0:3e:f1:85 root@lifelinux

The command ssh-keygen -t rsa initiated the creation of the key pair.
No passphrase your was entered.
After this is completed, two files generated. The private key was saved in .ssh/id_rsa and public key was saved in .ssh/id_rsa.pub
Copy the public key to .ssh/authorized_keys with command:

[root@lifelinux~]#cat .ssh/id_rsa.pub >> .ssh/authorized_keys

Step2: Edit SSH config

[root@lifelinux~]#vi /etc/ssh/sshd_config

Make sure that the following settings as shown:

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile      .ssh/authorized_keys
PasswordAuthentication no

Step3: Restart SSH service

[root@lifelinux~]#/etc/init.d/sshd restart

Please note that for Putty you will need to import the generated private key into puttygen and export it into a new private key. This is because Putty does not support the SSH generated private key.

The post Setting Up An SSH Certificate appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.