1, See release information

cat /etc/issue

2, Check the kernel version number

uname -r Check the kernel version number

uname -p Look at the processor type 32bit/64bit

uname -n View the network host name (or hostname)

3,OpenJDK and JDK What's the difference ?

Oracle JDK is based on the OpenJDK source code. In addition, it contains closed-source
components. in other words ,OpenJDK Removed JDK Some copyright issues are involved in API And the source code , Functional ratio JDK Less .

4, Father Shell、 Son Shell

When running a Shell Script when , Father Shell Will be based on Script The first line of the program #! Later specified Shell The program opens a child Shell Environmental Science , And then in the Shell Run this Shell Script. Once it's done Shell Medium Script Run complete , This son Shell And then it's over . Back to the father Shell in . It doesn't affect the father Shell The original environment . Son Shell Environment has and father Shell The same environment variable 、 The standard input 、 Output 、 Errors, etc .

source Command function ?

Able to use help source View help documents .P.S. Order and source command , Usage method: .
filename [arguments]

source: source filename [arguments]

Execute commands from a file in the current shell.

and execute commands from FILENAME in the current shell.  The entries in $PATH are used to find the directory containing
FILENAME.  If any ARGUMENTS are supplied, they become the positional parameters when FILENAME
is executed.

Exit Status:

Returns the status of the last command executed in FILENAME; fails if FILENAME
cannot be read.

file filename Can run without permission .

At present shell Run in and in sub shell The difference between the two is , The variables and functions defined by the latter disappear at the end of the run , And the former can survive . therefore , If we change /etc/profile What's in it , Such as adding environment variables . So if it's going to take effect immediately , Must use source Command or click command in the current shell I'm gonna run it in .

6, environment variable

(1) View all environment variables :

$ set

(2) Look at an environment variable :

$ echo "$PATH"

(3) Environment variable Settings :

export ANT_HOME=/path/to/ant/dir
export PATH=${PATH}:${ANT_HOME}/bin:${JAVA_HOME}/bin

(4) Persistent environment variable file :

/etc/profile, Where system level environment variables are stored , Valid for all users . After setting, you need to log in again to take effect .

~/.bashrc, The place where the current user environment variables are stored , Valid only for current users .

After setting, you just need to start it again shell.

Of course , It's described above source The order can take effect immediately .

Copyright notice : This article is an original blog article . Blog , Without consent , Shall not be reproduced .

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