(1) ln - Create file hard link, or soft link (symbolic link)
hard link:
ln /root/install.log x.hard
soft link:
ln -s /root/install.log x.soft
(2) shutdown - reboot the system
reboot the system now:
shutdown -r now
(3) pwd - show current working directory
(4) cd - change directory
(5) mkdir - make directory
(6) rmdir - remove directory
(7) ls - list files
list all files:
ls -al
(8) more - viewing files
view a file:
more a.txt
(9) cat - viewing files or concatenate files into one
view a file:
cat a.txt
(10) kill - raise a signal to a process
terminate a process:
kill -9 1447 (process id)
or
kill -9 %1 (sequence id)
(11) logout - login out of the system
(12) vi - text editor
(13) emacs - powerful editor & compiler
(14) cp - copy files
copy a to b:
cp a b
(15) mv - remove files
remove file:
rm a.txt
(16) echo - show information
show value of $PATH:
echo $PATH
(17) chsh - change shell
(18) who - show current users in memory
(19) date - show date and time
(20) export - create a enviroment variable
set enviroment variable:
export JM=ls
echo $JM
$JM
another way is simple:
JM=ls
(21) > - redirection to a file
save output to file:
cat a b c > d
(22) >> - append output to a file
append output to file:
cat a b c >> d
(23) & - background process operation
put work background:
gcc invinitjig.c &
(24) ps - show processes in memory
(25) fg - bring background processes forehead
(26) 1 and 2 usage - 1 stands for standard output, and 2 for standard error output
save error output:
cat notexistfile 2> err_file
save standard output:
cat existfile 1> out_file
(27) /dev/null - throw away output
throw away all output:
cat abc > /dev/null
(28) sort - sort strings
(29) du - stands for "disk usage" and shows how many blocks each file occupies under the current directory
(30) | - pipeline
(31) man - manual book
see manual of ls:
man ls
(32) info - read info doucments, stronger than man command
see info of grep:
info grep
(33) r/w/x - ownership of files: read / write / execute, left to right: owner/group/others
(34) chown - change owner of files
change owner:
chown jm filename
(35) chgrp - change group of files
(36) chmod - change file access mode
set r/w/x permission to all (owner/group/others):
chmod +x a.exe
chmod +r a.exe
chmod +w a.exe
chmod -x a.exe
chmod -r a.exe
chmod -w a.exe
specify the owner/group/others:
chmod u+r a.exe
chmod ug+r a.exe
(37) su - run a shell with substitute user and group IDs
(38) history - command history
(39) dd - Copy a file, converting and formatting according to the options
(40) alias - make alias name
eg.
alias x="ls"
x
(41) mount - 挂载分区或镜像文件(.iso,.img)文件。
用法：
磁盘分区：mount deviceName mountPoint -o options，其中deviceName是磁盘分区的设备名，比如/dev/hda1,/dev/cdrom,/dev/fd0，mountPoint是挂载点，它是一个目录，options是参数，如果分区是linux分区，一般不用-o options，如果是windows分区那options可以是iocharset=cp936，这样windows分区里的中文文件名就能显示出来了。
用例：比如/dev/hda5是linux分区，我要把它挂到目录a上（如没目录a那就先mkdir a），mount /dev/hda5 a，这样目录a里的东西就是分区hda5里的东西了，比如hda1是windows分区，要把它挂到b上，mount /dev/hda1 b -o iocharset=cp936。
镜像文件：
mount fileName mountPoint -o loop，fileName是镜像文件名(*.iso,*.img)，其它的不用说了，跟上面一样。
用例：如我有一个a.iso光盘镜像文件，mount a.iso a -o loop，这样进入目录a你就能浏览a.iso的内容了，*.img文件的用法一样。
(42) find - 查找文件。
用法：
find inDir -name filename，inDir是你要在哪个目录找，filename是你要找的文件名(可以用通配符)，用通配符时filename做好用单引号引起来，否则有时会出错，
用例：find . -name test*，在当前目录查找以test开头的文件。
(43) grep - 在文件里查找指定的字符串。
用法：
grep string filename，在filename(可用通配符)里查找string(最好用双引号引起来)。参数：-r在所有子目录里的filename里找。
用例：grep hello *.c -r在当前目录下（包括子目录）的所有.c文件里查找hello。
(44) tar - pack or unpack files
(45) netconfig - network configuration
(46) rpm - install softwares
(47) rdev - query/set image root device, RAM disk size, or video mode
(48) passwd - change password
(49) adduser - add a user
(50) userdel - delete a user
(51) umount - reverse to mount
(52) mkfs - build a Linux file system
(53) fsck - check and repair a Linux file system
(54) free - display information about free and used memory on the system
(55) makeswap - make swap
(56) swapon - swap on
(57) swapoff - swap off
(58) mknod - make block or character special files
(59) gzip - pack / unpack files
(60) crontab - scheduling jobs
(61) setterm - set terminal attributes