1. cd
cd ~username: The command is used to switch directories, and can also switch the user's home directory.
[root@localhost ~]# cd ~123
[root@localhost 123]# pwd #View the current path
/home/123
The user’s home directory is a folder created for a specific user. The user The user has ownership of the contents of this folder, but not all programs in the user's home directory belong to the user. The owner of the test2 file below is root, because it is a file created with root permissions, and a test2 with read-only permissions is created on the desktop.
[root@localhost Desktop]# touch test2
[root@localhost Desktop]# ls -l
total 2220
-rw-r--r--. 1 root root 2272130 Aug 6 2013 cacti-0.8. 8b.tar.gz
-rw-rw-r--. 1 123 123 0 Nov 1 03:38 new file
-rw-rw-r-- 1 123 123 0 Nov 17 22:42 new file (copy )
-rw-r--r-- 1 root root 0 Nov 17 23:16 test2
If you log in to the 123 user through su and create a test4 file, its owner belongs to the 123 user and has Read and write permissions.
[123@localhost Desktop]$ su 123
Password:
[123@localhost Desktop]$ ls
cacti-0.8.8b.tar.gz new file new file (copy) test2 test3
[123@ localhost Desktop]$ touch test4
[123@localhost Desktop]$ ls -l
total 2220
-rw-r--r--. 1 root root 2272130 Aug 6 2013 cacti-0.8.8b.tar.gz
-rw-rw-r--. 1 123 123 0 Nov 1 03:38 new file
-rw-rw-r-- 1 123 123 0 Nov 17 22:42 new file (copy)
-rw -r--r-- 1 root root 0 Nov 17 23:16 test2
-rw-rw-r-- 1 123 123 0 Nov 17 23:18 test3
-rw-rw-r-- 1 123 123 0 Nov 17 23:20 test4
2, type
The type of command can be realized through the type command. Commands in Linux are divided into internal commands and external commands.
[123@localhost Desktop]$ type cut
cut is /usr/bin/cut #External command (in a corresponding directory)
[123@localhost Desktop]$ type echo
echo is a shell builtin #Internal command
3, printenv
Through this command, you can view the environment variable information of the system. The environment variable information has the same meaning as the JAVA setting. Among a lot of information, only PATH is the environment variable information. . Newly developed programs must also be set in environment variables.
[root@localhost Desktop]# printenv
ORBIT_SOCKETDIR=/tmp/orbit-123
HOSTNAME=localhost.localdomain
TERM=xterm
SHELL=/bin/bash
XDG_SESSION_COOKIE=2604b 541bf302be0cd47ddec00000011-1479446380.885020-236895646
HISTSIZE=1000
GTK_RC_FILES=/etc/gtk/gtkrc:/home/123/.gtkrc-1.2-gnome2
WINDOWID=46138793
USER=123
LS_COLORS=rs=0:di=01; 34: ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31; 01:mi=01;05;37;41:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex= 01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.lzma=01; 31:*.tlz=01;31:*.txz=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31: *.gz=01;31:*.lz=01;31:*.xz=01;31:*.bz2=01;31:*.tbz=01;31:*.tbz2=01;31:*. bz=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.rar=01;31:*.ace= 01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.jpg=01;35:*.jpeg=01; 35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35: *.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*. svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v= 01;35:*.mkv=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01; 35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35: *.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*. xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.axv=01;35:*.anx= 01;35:*.ogv=01;35:*.ogx=01;35:*.aac=01;36:*.au=01;36:*.flac=01;36:*.mid=01; 36:*.midi=01;36:*.mka=01;36:*.mp3=01;36:*.mpc=01;36:*.ogg=01;36:*.ra=01;36: *.wav=01;36:*.axa=01;36:*.oga=01;36:*.spx=01;36:*.xspf=01;36:
GNOME_KEYRING_SOCKET=/tmp/keyring-ejyje6 /socket
SSH_AUTH_SOCK=/tmp/keyring-ejyje6/socket.ssh
SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/2354,unix/unix:/tmp/.ICE-unix/2354
USERNAME=123
DESKTOP_SESSION=gnome
MAIL=/var/spool/mail/123
PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin :/sbin:/home/123/bin
PWD=/home/123/Desktop
GDM_KEYBOARD_LAYOUT=us
LANG=en_US.UTF-8
GNOME_KEYRING_PID=2344
GDM_LANG=en_US.UTF-8
GDMSESSION=gnome
SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass
HISTCONTROL=ignoredups
HOME=/root
SHLVL=11
GNOME_DESKTOP_SESSION_ID=this-is-deprecated
LOGNAME=123
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-MMUi3C39vL,guid=b6fecbcb44a8fd92e501ec9b0000003d
LESSOPEN=|/usr/bin/lesspipe.sh %s
WINDOWPATH=1
DISPLAY=:0.0
G_BROKEN_FILENAMES=1
COLORTERM=gnome-terminal
_=/usr/bin/printenv
4 , hash
The hash command is used to display the number of times the command is tapped on the screen. hash -r is used to clear the cache information of this command. When the command used in the hash is used again, it will not be called in the kernel, but will be removed directly from the cached KV (key value) database, which will be very fast.
[root@localhost Desktop]# hash
hitscommand
1/bin/grep
1/bin/vi
1/usr/bin/man
2/usr/bin/printenv
1/usr /bin/clear
5, date
Display the system time. The system time here is the kernel time of the system. The kernel time is the simulated time oscillator for timing. After the system is installed, the hardware time of the host will be read, and then it will Time it yourself. Use date -u month day hour minute year. second to set the system time.
[root@localhost Desktop]# date -u 1118160216.30
Fri Nov 18 16:02:30 UTC 2016
The date command also includes some wildcard options, taking 2016/11/18 as an example, %y=16 ,%m=11,%d=18, when using wildcard fields, + must be added after date.
[root@localhost Desktop]# date
Fri Nov 18 16:11:13 PST 2016
[root@localhost Desktop]# date +%y
16
[root@localhost Desktop]# date +% m
11
[root@localhost Desktop]# date +%d
18
The output effect of changing the letters after the wildcard character to uppercase is like this
[root@localhost Desktop]# date +%Y
2016
[root@localhost Desktop]# date +%M
13
[root@localhost Desktop]# date +%D
11/18/16
date can also output text
[root @localhost Desktop]# date +"today is %d"
today is 18
[root@localhost Desktop]# date +"this year is %Y"
this year is 2016
6、clock,hwclock
As mentioned before, in addition to the date that can check the current time, there is also the hardware time that can be checked through the clock. The clock and date times may be different.
[root@localhost Desktop]# date
Fri Nov 18 16:22:02 PST 2016
[root@localhost Desktop]# clock
Fri 18 Nov 2016 12:22:45 AM PST -0.906975 seconds
The above system time is different from the hardware time. The system time is correct and can be modified through hwclock -w.
[root@localhost Desktop]# hwclock -w
[root@localhost Desktop]# clock
Fri 18 Nov 2016 04:24:43 PM PST -0.141483 seconds
[root@localhost Desktop]# date
Fri Nov 18 16:24:51 PST 2016
There is also a command cal to view the calendar of the current year, cal -y to view the specified year.
[root@localhost Desktop]# cal
November 2016
Su Mo Tu We Th Fr Sa
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
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