Linux Learning--the difference between Su and Su--deep analysis

the difference between Su-and Su--Interactive logon and non-interactive login

First, Brief introduction

Interactive : Enter the account password directly through the terminal login, etc.

variables, aliases, etc. won't inherits from the previous shell, it will be re-read

non-interactive : Open terminal under graphical interface, execute script, any other bash instance, etc.

variables, aliases, etc. will be inherit the upper-level shell and then read the file

Ii. Related Documents

Let's take a look at these five files. Main contents

/etc/profile : Storing environment variables that already exist in the system, such as Path,user

/etc/profile.d/*.sh : Storage of many color settings, vim settings, etc.

~/.bash_profile : The contents of the file refer to ~/.BASHRC

~/.BASHRC : The contents of the file refer to/ETC/BASHRC

/ETC/BASHRC : Setting variables related content

Profile class	The shell of the interactive logon provides the configuration
BASHRC class	Non-interactive and interactive logon shell provides configuration

File read order when user logs in:

Interactive: /etc/profile --/etc/profile.d/*.sh--and ~/.bash_profile--~/.BASHRC--/ETC/BASHRC

non-interactive: ~/.BASHRC ---/ETC/BASHRC-/etc/profile.d/*.sh

Three, combining case analysis

① Add export a=a1 to/etc/profile

Under/etc/profile.d/vim mage.sh, add content to export B=B2

Add Export c=c3 to ~lisi/.bash_profile (make sure Lisi this user exists)

Add Export d=d4 under ~LISI/.BASHRC

Add Export E=e5 under/ETC/BASHRC

Note: All variables are added in the first row, not including comment lines

② Re-login Su-root

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E (currently login root user, according to the file read order, so will skip ~lisi/.bash_profile and ~LISI/.BASHRC)

Results show: A1 B2 E5

③/etc/profile A1 changed to A6

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E (A6 is not displayed because a is a saved or last logged-in variable)

Results show: A1 B2 E5

④SU Root

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E (non-interactive login root, in the non-interactive read file order, will also skip ~LISI/.BASHRC, the current non-interactive (child shell) will inherit the previous level of login shell, so a is the value of A1)

results show: A1 B2 E5

⑤exit (exit the child shell and return to the upper shell, that is, Su Root enters a child shell)

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E

Results show: A1 B2 E5

⑥vim/etc/profile.d/mage.sh Change B2 to B7

su Root (/etc/profile.d/mage.sh will be read in non-interactive order)

Results show: A1 B7 E5

⑦exit

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E

Results show: A1 B2 E5

⑧su Lisi

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E

Results show: A1 B7 D4 E5

⑨exit

Su-lisi

Echo $A, Echo $B, Echo $C, Echo $D, Echo $E (in interactive read order, and interactive does not inherit variables from the previous login shell)

Results show: A6 B7 C3 D4 E5

Small tip: execution scripts are also run under a child shell, which inherits the variables of the parent shell (non-interactive)

Parent shell cannot inherit files from child shell

The above has been said: execution scripts are also non-interactive logins, variables defined in the script do not take effect outside the script (under the parent shell)

but source+ Script or . + Script is to run under the current shell (under the parent shell) and the bash+ Script (under sub-shell) There are essential differences between the methods

Linux Learning--the difference between Su and Su--deep analysis