, Iptables -Z empty recounting
How memory works? You are doing?
Also known as random access memory " RAM ",an internal memory direct exchange with the CPU, also called main memory. It can read and write at any time, and fast, usually asthe operating systemor other programs that are running in the temporary data storage media.
Volatile:
when the power is turned off RAM can retain data. If you need to save the data, you must write them a long-term storage device (such as a hard disk). RAM and ROM, the biggest difference is in RAM after a power failure to save the above data will automatically disappear, and ROM will not.
> Gnu software program
> Linux lernel kernel
> Gcc Gnu Compiler Suite
> Android system is based on the underlying Linux is based on C and C ++, most upper application is based on " JAVA" of.
> Operating system work process:
Shell default program : bash
(Kernel memory management CPU IO (bus, peripherals))
> What are the hard links and soft links
Hard links: (inode) to generate a new file name through the file system, rather than create a new profile.
Soft Link: seen as a shortcut in Windows that lets you quick links to the target file or directory
> Shell script basis:
Look ban Chinese manual
builtin built
alias alias
bind binding
exec execution
bin directory to store binary files
The history of commands before viewing history
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The representative of the Hidden
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crontab to do regular tasks
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> History of command
-d Delete the specified row
-c will present all the shell of the history command elimination. It has no effect on command history file
-a: the current record information, add to /root/.bash_history
! View command:
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Restart the service:
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-x execute permissions
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Date command:
It displays the current system time (hardware clock) NTP server
Clock 、hwclock
[] Optional Optional parameter is optional
Format format
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> Note that `` (Kin tab is on top of)
Backup cycle:
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Total ASCII code 256, the former 128 ( 0 to 127) is called the base ASCII; after 128 ( 128 to 255) is called extended ASCII codes. Each ASCII code occupies one byte ( Byte), and each byte consisting of 8 bits ( composed Bit).
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:( compressed file set-up time)
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which tar file path View
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crontab write full path
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crontab -e to do a backup
Minute Hour few numbers a few months a few numbers of the week
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Command execution status
$?
After the command is executed, the return value of two categories:
1. Name of the default return value
2. Command execution status of
There are two types of state:
1,0 - on behalf of the command was successful
2, 1-255-- represent failed
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127 represents the command can not find
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$? Special environment variable used to execute a command on the memory status
[$? –eq 0]&& exit 0 || exit 1
Command shortcuts:
Ctrl + a beginning of the line
Ctrl + e end of the line
U put before deleting
After the deleting K
W delete a string
New graphics terminal Shift + t
L clear
S lock screen
Q unlock
D Close the current bash program
R calling a match recently String command