I'm new to linux. And I'm confused with the different shell titles in linux.
for example, when I called "/bin/sh", I saw
sh-3.1#
but when I used "su root", I saw
my-environment:~#
and when I logged in as normal user, I saw
user#my-environment:$
I kind of notice # means root and $ means non-root, but could some explain how I got the above titles?
Thanks a lot!
The text at the shell prompt is controlled by the variable $PS1 (and sometimes $PS2 $PS3 $PS4). This blogpost explains how you can customize the prompt in many ways.
Do echo $PS1 in the different terminals to see the current value.
This depends on your variable environment $PS1.
To see what I mean, try doing PS1=something, and see what happens.
To reset it you could do source ~/.bashrc.
So, why do you have different prompt according? Because you don't load the same files according to the command you type to open your sessions, so you end up with different configs, hence a different $PS1
Related
EDIT
The answer to my question is actually obvious, I simply forgot about the meaning of the EXPORT keyword. I still drop the explanation here, just in case.
So in a few words, when opening a terminal with Ctrl-Alt T a new shell is created, which is a child of the shell created at loggin. As explained here, the loggin shell is initialized by reading /etc/profile, and as explained here and more specifically here elements of the environment are transmitted to child processes, notably variables prefixed with the EXPORT keyword.
I am trying to understand what is the mechanism under which the PATH is set under linux when opening a new (virtual) terminal.
I know one can change the PATH in several files (e.g. system : /etc/{profile, bash.bashrc, ... } or user: ~/{.profile, .bash_login, .bashrc... }, some of which are read at login, the others when opening new (virtual) terminals.
According to my tests, it seems the "profile" files are read at startup (when the user logs in), which registers some startup values for variables such as PATH. Then, each time a terminal is opened these startup values are provided to other script (e.g. bashrc) for further configuration, resulting in something like : PATH_IN_TERMINAL=$BASHRC_ADDONS:$PATH_FROM_PROFILE
Notably, ~/.profile won't normally be read after login. Changing this file won't have any effect in the current session and the PATH_FROM_PROFILE part of the PATH will remain the same until one logs in again (after logout or through ssh connection for instance).
Am I correct ? And if so, where can I find a doc on the subject ?
Thanks
This is the best explanation I have found on the subject: Startup Files
The simple explanation, in most common situations is:
Upon initial login to host, read /etc/profile followed by the first of
~/.bash_profile, ~/.bash_login or ~/.profile. ~/.profile is
supported by multiple shells, so is preferred.
When Bash starts, but not immediately after login, read ~/.bashrc.
So, profile files are intended to run upon login and should be used to print initial messages (e.g. Security Warning, Message of the Day), check mail, and configure settings/variables that rarely change. Either system-wide (quotas, MOTD, etc.), or user-specific (timezone, locale, terminal, etc.).
.bashrc files are intended for individual users to customize their interactive experience. e.g. defining aliases, setting prompts, adding to PATH, etc.
I almost always add source ~/.bashrc to the end of my .profile file so that my shell is always customized to my requirements, even immediately after login.
NOTE: The above only applies to interactive shells (e.g. running on a terminal). None of these files are read if bash is run non-interactively (e.g. via cron). In those cases, you should create a different file containing required variables and specify that via the BASH_ENV environment file.
I'm doing some work using Linux server, after I log on to the server,the tutorial says:
If you need to run any program which will open a window, like xterm, from these servers, you need to set display first.
To do that, I need to execute setenv DISPLAY name:portnum.What does this command really do?If I don't execute this command,what will happen?And what is xterm?
setenv is specific and peculiar to csh and derivatives. The modern portable syntax is
DISPLAY=:0.0
though if your shell is csh or tcsh, this will not work, and you do need setenv after all.
Depending on the use case, you may need to export DISPLAY as well.
Environment variables are a simple way to pass configuration information between programs. The DISPLAY variable indicates to graphical programs on which screen or graphical terminal to display their GUI.
For X Window System, it is a server/client architecture, usually, server side is called display, the tutorials means you should launch server side and specify launch parameter for server side.
read here for more details.
Xterm is just a terminal. And setenv, is used to set Environment variables, which are basically variables used to define the behavior of the terminal. For example, you have the variable PATH, which is used by the terminal to find the path where to execute binaries. Because if you type the command "ls", your terminal has to go into the "env", look for the variable "PATH", and use the value stored in this variable "PATH" to find the path of the ls binary. But I don't know if it's necessary in your situation, could you give more details about the context?
This question already has answers here:
How to permanently set $PATH on Linux/Unix [closed]
(24 answers)
Closed 6 years ago.
This is a very interesting question that I stumbled upon when I was creating a command-line application tool for Linux. Unfortunately, the answer on SO is so hidden among the myriad answers to other questions that I decided to ask another question on SO for those who want to modify PATH programmatically.
Grzegorz Żur's answer to another question captures it brilliantly. Unfortunately it was hidden away among many other answers.
There are multiple ways to do it. The actual solution depends on the
purpose.
The variable values are usually stored in either a list of assignments
or a shell script that is run at the start of the system or user
session. In case of the shell script you must use a specific shell
syntax.
System wide
/etc/environment List of unique assignments. Perfect for adding system-wide directories like /usr/local/something/bin to PATH
variable or defining JAVA_HOME.
/etc/xprofile Shell script executed while starting X Window System session. This is run for every user that logs into X Window
System. It is a good choice for PATH entries that are valid for
every user like /usr/local/something/bin. The file is included by
other script so use POSIX shell syntax not the syntax of your user
shell.
/etc/profile and /etc/profile.d/* Shell script. This is a good choice for shell-only systems. Those files are read only by shells.
/etc/<shell>.<shell>rc. Shell script. This is a poor choice because it is single shell specific.
Also, /etc/environment is not a script file, but rather consists of assignment expressions, one per line. Since this file stores the system-wide locale and path settings, it is most oft quoted choice.
Using /etc/profile is not preferred. It exists only to point to /etc/bash.bashrc and to collect entries from /etc/profile.d
User session
~/.pam_environment. List of unique assignments. Loaded by PAM at the start of every user session irrelevant if it is an X
Window System session or shell. You cannot reference other variable
including HOME or PATH so it has limited use.
~/.xprofile Shell script. This is executed when the user logs into X Window System system. The variables defined here are visible to
every X application. Perfect choice for extending PATH with values
such as ~/bin or ~/go/bin or defining user specific GOPATH or
NPM_HOME. The file is included by other script so use POSIX shell
syntax not the syntax of your user shell. Your graphical text editor
or IDE started by shortcut will see those values.
~/.profile Shell script. It will be visible only for programs started from terminal or terminal emulator. It is a good choice for
shell-only systems.
~/.<shell>rc. Shell script. This is a poor choice because it is single shell specific.
For temporary change:
~$ export PATH=$PATH:~/root/scripts
For permanent change, you can add this line to the /etc/environment file like this:
PATH=$PATH:~/root/scripts
I have a program, let's call it exampleProg, in my /opt directory, and I want to run it from any directory, rather than just:
/opt/radFolder/exampleProg
This should be a simple task, I've done it several times before on different computers. I've searched around, and found instructions ranging from:
edit .bash
edit .bashrc
edit .profile (Another stackoverflow answer said that, while this worked at one time, it no longer functions.)
edit /etc/environment/
with PATH="$HOME/bin:$PATH:/opt/radFolder/:" or just adding the /opt/radFolder bit.
Yet none of them seem to work. The problem that I'm running into is that there doesn't seem to be a yet there doesn't seem to be a universally agreed-upon solution. I've tried so many that I think one of my changes has prevented the appropriate one from taking effect. Would someone help me put this to rest once and for all? Many thanks in advance.
I'm running ubuntu 14.04 LTS x64.
First, understand that writing things to those files does not mean everything is instantaneously, and globally, changed. In fact, nothing is changed until the file is sourced (via . or source), and even then, the environment changes apply only to the current shell (and subsequent created children, if export is used).
INVOCATION, near the top of man bash, spells out which files are automatically sourced when. To summarize:
~/.bashrc is read for new non-login, interactive shells, e.g., when you open a GUI terminal. On many systems, this file by default in turn sources /etc/bashrc.
/etc/profile, ~/.bash_profile, and ~/.profile are read by interactive login shells.
Adding to ~/.bashrc should be effective, but it will only work for subsequently invoked, interactive, non-login shells (and their children, if $PATH is exported). However, since it's prone to being sourced repeatedly, using it to add to an existing variable (as with $PATH) can produce repeated concatenations (see here).
An issue with the second category, .profile, is that if you use a GUI login, the display manager may not source it, but it logs you in, meaning, you never invoke a login shell and hence none of those is ever sourced. If this is the case, sourcing them from ~/.xsession should work (this has a system wide correlate in /etc/X11).
After I make changes in .bash_rc or .bash_profile, when I start GNU screen, it doesn't recognize those changes.
I can
source ~/.bash_profile
and it works for the current screen window I have open, but I have to do that for every screen window I have open.
How do I get screen to read my latest changes in my bash configuration?
If you want screen to always treat your shell as a login shell, and source the same files that would be read if just started a new shell normally, add the following to ~/.screenrc (or maybe ~/.byobu/.screenrc, as pointed out in the comment):
shell -$SHELL
This way, you don't need to manually tell it to source your files each time you start a new screen. Though you would have to if you just made changes and wanted those changes to be reflected in your current screen.
The documentation for this (and lots of other screen details) can be found here. Basically, shell is a command to screen telling it to run the following when it needs to create a new shell. $SHELL is the usual variable holding the path to your preferred shell. And the dash - in front of $SHELL indicates that it should be run as a login shell (which will typically mean it sources your ~/.bash_profile, etc.).
It's worth pointing out, however, that screen defaults to just inheriting most environment variables from the shell where you start screen; and a login sub-shell may alter some environment variables in unexpected ways. I ran into a situation where elements of my $PATH were basically permuted. I solved the problem thanks to this particularly excellent answer on superuser.
You may notice the source command available. It's important to note that this sources a file of screen commands, rather than shell commands. Other relevant (screen) commands include eval and exec.
You have to do it in each screen that you have open since they are all different shells. If you need the change every time a new shell is opened, I suggest you put the changes in ~/.bashrc instead.
Apparently, you can send a command to all windows at once using this syntax:
C-a :
at "#" stuff "source ~/.bash_profile^M"