Very useful Linux Commands

Very useful Linux commands: Ruby

Determine whether a user exists. create a user if the user does not exist

User = 'grep' ^ admin: '/etc/passwd'

If [-z "$ user"]; then

Groupadd admin

Useradd-d/home/admin-s/bin/bash-g admin

Echo '200' | passwd -- stdin admin

Echo '200' | passwd -- stdin root

Fi

Increasing file system space

Umount/home

E2fsck-f/dev/mapper/VolGroup-lv_home

Resize2fs-p/dev/mapper/VolGroup-lv_home 10G

Mount/home

Lvreduce-L 10G/dev/mapper/VolGroup-lv_home

Vgdisplay

Lvextend-L + 210.5G/dev/mapper/VolGroup-lv_root

Resize2fs-p/dev/mapper/VolGroup-lv_root

Common VI commands

: 50, 70 s/^/# Comment 50 to 70 rows

: 0, $ d delete all content

: % S/r // g press enter to delete DOS ^ M

: % S/^ (. *) n1/1 $/delete duplicate rows

: <

View the file size in the current directory, in ascending order

Du-sh * | sort-nr | head

Multi-IP, gateway configuration

/Sbin/ifconfig eth0: 1 192.168.13.122 netmask 255.255.255.0 up

/Sbin/route del default gw 192.168.12.1

/Sbin/route add default gw 192.168.12.1

Synchronization time

/Usr/sbin/ntpdate 192.168.12.1;/sbin/hwclock-w

Cancel your have mail in/var/spool/mail/root prompt

Echo "unset MAILCHECK">/etc/profile

Password-free logon

Ssh-keygen creates the public key and key.

Ssh-copy-id copies (append) the public key of the local host to the authorized_keys file of the remote host.

The ssh-copy-id will also be sent to the user home directory (home) and ~ of the remote host ~ /. Ssh, and ~ /. Ssh/authorized_keys set the appropriate permissions

Make sure that the configuration in/etc/ssh/sshd_config is AuthorizedKeysFile. ssh/authorized_keys.

Step 1: Use ssh-key-gen to create a public key and a key on the local host

Ligh @ local-host $ ssh-keygen-t rsa

Step 2: Use ssh-copy-id to copy the public key to the remote host.

Ligh @ local-host $ ssh-copy-id-I ~ /. Ssh/id_rsa.pub root@192.168.0.3

[Note: The ssh-copy-id appends the key to. ssh/authorized_key of the remote host.]

Step 3: log on to the remote host directly

Ligh @ local-host $ ssh root@192.168.0.3.

Test disk IO

Read performance test

# Time dd iflag = direct, nonblock if =/dev/sda2 of =/dev/null bs = 8 k count = 8388608

Because/dev/sda2 is a physical partition, reading it will generate IO,/dev/null is a pseudo device, which is equivalent to a black hole, of this device will not generate IO, so, the IO of this command only occurs on/dev/sdb1, which is equivalent to testing the disk's read capability.

Write test

# Time dd oflag = direct, nonblock if =/dev/zero f =/opt/iotest bs = 8 k count = 8388608

Because/dev/zero is a pseudo-device, it only generates a null compaction stream and does not generate IO for it. Therefore, IO will be concentrated in the of file, and the of file is only used for writing, therefore, this command is equivalent to testing the disk write capability.

Read/write test

# Time dd iflag = direct, nonblock oflag = direct, nonblock if =/dev/sda2 f =/opt/iotest bs = 8 k count = 8388608

Mysql installation

Create the mysql installation directory and database storage directory

[Root @ rhel5 ~] # Mkdir-p/usr/local/mysql // install mysql

[Root @ rhel5 ~] # Mkdir-p/usr/local/mysql/data // store the database

Create mysql users and user groups

[Root @ rhel5 ~] Groupadd mysql

[Root @ rhel5 ~] Useradd-r-g mysql

Install mysql

# Tar-zxv-f mysql-5.5.10.tar.gz

# Cd mysql-5.5.10

# Cmake.

-DCMAKE_INSTALL_PREFIX =/usr/local/mysql

-DMYSQL_DATADIR =/usr/local/mysql/data

-DDEFAULT_CHARSET = utf8

-DDEFAULT_COLLATION = utf8_general_ci

-DEXTRA_CHARSETS = all

-DENABLED_LOCAL_INFILE = 1

# Make

# Make install

Install and configure JDK

Tar zxvf jdk1.6.0_25.tar.gz-C/export/servers/

Vi/etc/profile

Add as follows:

Export JAVA_HOME =/export/servers/jdk1.6.0 _ 25

Export JAVA_BIN =/export/servers/jdk1.6.0 _ 25/bin

Export PATH =/$ PATH:/$ JAVA_HOME/bin

Export CLASSPATH =.:/$ JAVA_HOME/lib/dt. jar:/$ JAVA_HOME/lib/tools. jar

Export JAVA_OPTS = "-Djava. library. path =/usr/local/lib-server-Xms1024m-Xmx2048m-XX: MaxPermSize = 256 m-Djava. awt. headless = true -Dsun.net. client. defaultReadTimeout = 60000-Djmagick. systemclassloader = no-Dnetworkaddress. cache. ttl = 300 -Dsun.net. inetaddr. ttl = 300"

Export JAVA_HOME JAVA_BIN path classpath JAVA_OPTS

Killing all processes

Ps-ef | grep $1 | grep-v grep | awk '{print $2}' | xargs kill-9

Uninstall openjdk

View

Rpm-qa | grep java

Uninstall:

Rpm-e -- nodeps java-1.6.0-openjdk-devel-1.6.0.0-1.45.1.11.1.el6.x86_64

Rpm-e -- nodeps java-1.5.0-gcj-1.5.0.0-29.1.el6.x86_64

Rpm-e -- nodeps java-1.6.0-openjdk-1.6.0.0-1.45.1.11.1.el6.x86_64

Force unloading:

Rpm-qa | grep software name | while read line; do rpm-e -- allmatches -- nodeps $ line; done

Soft link:

Ln-s/export/servers/jdk1.6.0 _ 25/bin/jar/usr/bin/jar

Ln-s/export/servers/jdk1.6.0 _ 25/bin/javac/usr/bin/javac

Source/etc/profile

View:

Java-version