Linux command-system application command
Linux commands--system application commands
1. Time management
date: Display system time
clock: Display hardware time
hwclock -W: Synchronizes system time to hardware time
hwclock -s: synchronizes hardware time to system time
cal: Display calendar
Date of modification:
The order dated 9 January 1996 reads as follows:
#date -s 1/9/2009
Date and time set: August 8, 2008 12:00
date -s "2008-08-08 12:00:00"
Set the time to 14:36 p. M.
date -s 14:36:00
Remember to synchronize bios time after changing the time:
Synchronizing the BIOS clock forces the system time to be written to CMOS with the following commands:
#clock -w
2. Help orders
Internal command help: help COMMAND
External Command Help: man COMMAND
Command manual: manual
whatis COMMAND: Shows which section of man help this command is in.
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The man's command:
Space: Flip back one screen
b: Turn forward one screen
ENTER: Turn back one line
k: forward one line
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key lookup
/KEYWORD: search keywords backwards
？KEYWORK: Search keywords forward
n: Next keyword position
N: previous keyword
Q: Exit man help
3. System information
switch directory
cd Back to user's home directory
cd ~username: Enter the specified user's home directory
cd -: toggles between the current directory and the previous directory
cd ..: Switch to its parent directory
cd /home Go to '/ home' directory '
4、alise
Define aliases for shell commands
alias CMDALIAS=COMMAND
unalias CMDALIAS is an alias for the undo command
5、printenv
Display current variable information
6、whoami
Show who the current user is
su -: When switching, the user before switching is displayed
7、who
View the user currently logged into the system and the terminal he logged into
-r: Displays the current operating level
-H: The first time the list shows the column names
w: Display more detailed information than who
8、last
Displays the login log (/var/log/wtmp file) on the current system, including system user and restart information
last -n number: only shows the most recent login information
9、lastb
Show user error login common sense
lastb -n Number: Displays only the last few wrong logins
10、lastlog
Displays information about each user's last successful login
lastlog -u USERNAME: Displays the last login information of the specified user
11、basename
Displays the base name of a directory
basename /etc/abc/me Show me directly
$0: Command name or path to script itself.
basename $0: Call script path directly
12、mail
Mail view, you can view mail, after viewing will be placed in the user's home directory mbox folder.
-s theme
mail -s "How are you " root
cat /etc/fast | mail -s "How are you " root
13、hostname
hostname: Displays the name of the current host
hostname hostname: change hostname
14、fuser
Verify that the file or socket in use is being used
-v: View processes in use on a file
-k: Give the visiting process to kill
-km: Shut down all processes on the mount point
15、watch
Periodically execute specified commands and display results in full screen mode
Format: watch -n # 'COMMAND'
-n #: Specify the cycle, unit is seconds, default is 2 seconds
16、ps
View process information
BSD style common options:
a: Display all terminal-related processes?: It is not related to the terminal.
x: Displays all processes unrelated to the terminal
u: Display progress information
aux: combined use
SysV style common options:
-elF: View all progress information (e: All progress)
F: No details.
-o PROPERTY: Specifies property display
17、top
Dynamic display of process information
Support interactive, interactive commands
M: Sort by resident memory size
P: Sort by percentage of CPU usage
T: Sort by cumulative time
l: Whether average load and startup time are displayed
t: Whether to display information related to progress and CPU status
m: Whether to display memory-related information
c: Does the full command line information appear?
Q: Exit top
k: Terminate a process
Common options:
- d1: Refresh every few seconds
-b: batch mode display
-n #: How many batches are displayed in batch mode
18, foreground and background
foreground job: occupies command prompt
Background jobs: After startup, the command prompt is released, and subsequent operations are completed in the background
Front Desk--> Backstage:
Ctrl+Z: Send jobs to background
bg: Keep jobs stopped in the background running
bg [%JOBID]:% can be saved
fg: Send foreground jobs to background
fg [%JOBID]: % Can save SysV style common options:
-elF: View all progress information (e: All progress)
F: No details.
-o PROPERTY: Specifies property display
19、shutdown
shutdown [-akrhHPfnc] [-t secs] time [warning message]
shutdown: Command to shut down
-r now: restart immediately
-t sec: a few seconds later
-h now: shut down immediately
20、uname
uname -r: View system kernel version
uname -a: System version information
21、dd
Convert and copy files, copying the lowest data stream
Format: dd if= data source of= data storage destination bs=#how large is a unit count=#copy
How many times does this data
for example
dd if=/dev/sda of=/mnt/usb/mbr.backup bs=512 count=1
Can be used to backup MBR
Create Loop File
dd if=/dev/zero of=/var/swapfile bs=1M count=1024 This command creates a 1G image file, which can be directly mkswap and can be started.
/dev/zero is a bubble device that spits zeros out all the time
22、mktemp
mktemp: Create temporary files
mktemp /tmp/file.XX(XX stands for files automatically generated by the system) Generate temporary files
mktemp -d /tmp/file.xx: Generate temporary directory
23、at
at: Specify a task to be performed at some point in the future
time format
Absolute time: HH:MM DD:MM:YY MM/DD/YY
Relative time: now+#(minutes,hours,days,weeks)
Blur time: noon,midnight,teatime
at -l: Display your list of assignments
at -d Job Number: Delete Job
24、cron
cron: uninterrupted permitted service
System cron definition format:
Minutes Hours Days Months Weeks User Tasks
User cron task definition format
Definition file/var/spool/cron/USERNAME
Format: Minute Hour Day Month Week Task
