交互 Shells 和登录 Shells

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提出疑问

摘自 Interactive and Login Shells:

  • It doesn't seem like it's possible for there to be a login shell but not interactive.
  • Cron shell scripts are always non-login and non-interactive.
  • SSH shells are always login and interactive.
  • Subshells are always interactive but not login.
  • Shell scripts are always non-login and non-interactive.
  • Initial TTY shell should be login and interactive.

Swtching users inside Linux involves creating subshells, can you elect to switch without logging in, or switch while simulate the logging in process. Note that logging in doesn’t necessarily mean you need to enter passwords, nor that any password to be entered is possessed by the user you’re logging into.

Since .bashrc is read on interactive but not login, and .bash_profile is read on all login shells. People source the .bashrc in the .bash_profile, allowing you to set general configuration (that applies to all interactive shells) inside .bashrc but login specific configuration in .bash_profile.

略加思索

下面为具体的解释, 以及不同情况下启动脚本的加载顺序. (来自 login/non-login and interactive/non-interactive shells)

  • login shell: A login shell logs you into the system as a spiecified user, necessary for this is a username and password. When you hit ctrl+alt+F1 to login into a virtual terminal you get after successful login: a login shell (that is interactive). Sourced files:
    • /etc/profile and ~/.profile for Bourne compatible shells (and /etc/profile.d/*)
    • ~/.bash_profile for bash
    • /etc/zprofile and ~/.zprofile for zsh
    • /etc/csh.login and ~/.login for csh
  • non-login shell: A shell that is executed without logging in, necessary for this is a current logged in user. When you open a graphic terminal in gnome it is a non-login (interactive) shell. Sourced files:
    • /etc/bashrc and ~/.bashrc for bash
  • interactive shell: A shell (login or non-login) where you can interactively type or interrupt commands. For example a gnome terminal (non-login) or a virtual terminal (login). In an interactive shell the prompt variable must be set ($PS1). Sourced files:
    • /etc/profile and ~/.profile
    • /etc/bashrc or /etc/bash.bashrc for bash
  • non-interactive shell: A (sub)shell that is probably run from an automated process you will see neither input nor outputm when the calling process don’t handle it. That shell is normally a non-login shell, because the calling user has logged in already. A shell running a script is always a non-interactive shell, but the script can emulate an interactive shell by prompting the user to input values. Sourced files:
    • /etc/bashrc or /etc/bash.bashrc for bash (but, mostly you see this at the beginning of the script: [ -z "$PS1" ] && return. That means don’t do anything if it’s a non-interactive shell)
    • depending on shell; some of them read the file in the $ENV variable

识破

那么如何判断当前 shell 为 interactive 或 login shell 呢?