Environment variables
An environment variable is a named object that contains data used by one or more applications. In simple terms, it is a variable with a name and a value. The value of an environmental variable can for example be the location of all executable files in the file system, the default editor that should be used, or the system locale settings. Users new to Linux may often find this way of managing settings a bit unmanageable. However, environment variables provide a simple way to share configuration settings between multiple applications and processes in Linux.
Contents
Utilities
The coreutils package contains the programs printenv and env. To list the current environmental variables with values:
The env utility can be used to run a command under a modified environment. The following example will launch xterm with the environment variable EDITOR set to vim . This will not affect the global environment variable EDITOR .
The Bash builtin set allows you to change the values of shell options and set the positional parameters, or to display the names and values of shell variables. For more information, see the set builtin documentation.
Each process stores their environment in the /proc/$PID/environ file. This file contains each key value pair delimited by a nul character ( \x0 ). A more human readable format can be obtained with sed, e.g. sed ‘s:\x0:\n:g’ /proc/$PID/environ .
Defining variables
Globally
Most Linux distributions tell you to change or add environment variable definitions in /etc/profile or other locations. Keep in mind that there are also package-specific configuration files containing variable settings such as /etc/locale.conf . Be sure to maintain and manage the environment variables and pay attention to the numerous files that can contain environment variables. In principle, any shell script can be used for initializing environmental variables, but following traditional UNIX conventions, these statements should only be present in some particular files.
The following files should be used for defining global environment variables on your system: /etc/environment , /etc/profile and shell specific configuration files. Each of these files has different limitations, so you should carefully select the appropriate one for your purposes.
- /etc/environment is used by the pam_env module and is shell agnostic so scripting or glob expansion cannot be used. The file only accepts variable=value pairs. See pam_env(8) and pam_env.conf(5) for details.
- /etc/profile initializes variables for login shells only. It does, however, run scripts and can be used by all Bourne shell compatible shells.
- Shell specific configuration files — Global configuration files of your shell, initializes variables and runs scripts. For example Bash#Configuration files or Zsh#Startup/Shutdown files.
In this example, we add
/bin directory to the PATH for respective user. To do this, just put this in your preferred global environment variable config file ( /etc/profile or /etc/bash.bashrc ):
Per user
You do not always want to define an environment variable globally. For instance, you might want to add /home/my_user/bin to the PATH variable but do not want all other users on your system to have that in their PATH too. Local environment variables can be defined in many different files:
/.pam_environment is the user specific equivalent of /etc/security/pam_env.conf [1], used by pam_env module. See pam_env(8) and pam_env.conf(5) for details.
To add a directory to the PATH for local usage, put following in
To update the variable, re-login or source the file: $ source
/.bashrc etc. This means that, for example, dbus activated programs like Gnome Files will not use them by default. See Systemd/User#Environment variables.
Reading
/.pam_environment is deprecated and the feature will be removed at some point in the future.
Graphical environment
Environment variables for Xorg applications can be set in xinitrc, or in xprofile when using a display manager, for example:
The factual accuracy of this article or section is disputed.
/.config/environment.d/ on Wayland sessions is GDM-specific behavior. (Discuss in Talk:Environment variables)
Applications running on Wayland may use systemd user environment variables instead, as Wayland does not initiate any Xorg related files:
To set environment variables only for a specific application instead of the whole session, edit the application’s .desktop file. See Desktop entries#Modify environment variables for instructions.
Per session
Sometimes even stricter definitions are required. One might want to temporarily run executables from a specific directory created without having to type the absolute path to each one, or editing shell configuration files for the short time needed to run them.
In this case, you can define the PATH variable in your current session, combined with the export command. As long as you do not log out, the PATH variable will be using the temporary settings. To add a session-specific directory to PATH , issue:
Examples
The following section lists a number of common environment variables used by a Linux system and describes their values.
- DE indicates the Desktop Environment being used. xdg-open will use it to choose more user-friendly file-opener application that desktop environment provides. Some packages need to be installed to use this feature. For GNOME, that would be libgnomeAUR ; for Xfce this is exo . Recognised values of DE variable are: gnome , kde , xfce , lxde and mate .
The DE environment variable needs to be exported before starting the window manager. For example: This will make xdg-open use the more user-friendly exo-open, because it assumes it is running inside Xfce. Use exo-preferred-applications for configuring.
- DESKTOP_SESSION is similar to DE , but used in LXDE desktop environment: when DESKTOP_SESSION is set to LXDE , xdg-open will use PCManFM file associations.
- PATH contains a colon-separated list of directories in which your system looks for executable files. When a regular command (e.g. ls, systemctl or pacman) is interpreted by the shell (e.g. bash or zsh), the shell looks for an executable file with the same name as your command in the listed directories, and executes it. To run executables that are not listed in PATH , a relative or absolute path to the executable must be given, e.g. ./a.out or /bin/ls .
- HOME contains the path to the home directory of the current user. This variable can be used by applications to associate configuration files and such like with the user running it.
- PWD contains the path to your working directory.
- OLDPWD contains the path to your previous working directory, that is, the value of PWD before last cd was executed.
- TERM contains the type of the running terminal, e.g. xterm-256color . It is used by programs running in the terminal that wish to use terminal-specific capabilities.
- MAIL contains the location of incoming email. The traditional setting is /var/spool/mail/$LOGNAME .
- ftp_proxy and http_proxy contains FTP and HTTP proxy server, respectively:
- MANPATH contains a colon-separated list of directories in which man searches for the man pages.
- INFODIR contains a colon-separated list of directories in which the info command searches for the info pages, e.g., /usr/share/info:/usr/local/share/info
- TZ can be used to to set a time zone different to the system zone for a user. The zones listed in /usr/share/zoneinfo/ can be used as reference, for example TZ=»:/usr/share/zoneinfo/Pacific/Fiji» . When pointing the TZ variable to a zoneinfo file, it should start with a colon per the GNU manual.
Default programs
- SHELL contains the path to the user’s preferred shell. Note that this is not necessarily the shell that is currently running, although Bash sets this variable on startup.
- PAGER contains command to run the program used to list the contents of files, e.g., /bin/less .
- EDITOR contains the command to run the lightweight program used for editing files, e.g., /usr/bin/nano . For example, you can write an interactive switch between gedit under X or nano, in this example:
- VISUAL contains command to run the full-fledged editor that is used for more demanding tasks, such as editing mail (e.g., vi , vim, emacs etc).
- BROWSER contains the path to the web browser. Helpful to set in an interactive shell configuration file so that it may be dynamically altered depending on the availability of a graphic environment, such as X:
Using pam_env
The PAM module pam_env(8) loads the variables to be set in the environment from the following files: /etc/security/pam_env.conf , /etc/environment and
- /etc/environment must consist of simple VARIABLE=value pairs on separate lines, for example:
- /etc/security/pam_env.conf and
/.pam_environment share the same following format: @
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Переменная PATH в Linux
Когда вы запускаете программу из терминала или скрипта, то обычно пишете только имя файла программы. Однако, ОС Linux спроектирована так, что исполняемые и связанные с ними файлы программ распределяются по различным специализированным каталогам. Например, библиотеки устанавливаются в /lib или /usr/lib, конфигурационные файлы в /etc, а исполняемые файлы в /sbin/, /usr/bin или /bin.
Таких местоположений несколько. Откуда операционная система знает где искать требуемую программу или её компонент? Всё просто — для этого используется переменная PATH. Эта переменная позволяет существенно сократить длину набираемых команд в терминале или в скрипте, освобождая от необходимости каждый раз указывать полные пути к требуемым файлам. В этой статье мы разберёмся зачем нужна переменная PATH Linux, а также как добавить к её значению имена своих пользовательских каталогов.
Переменная PATH в Linux
Для того, чтобы посмотреть содержимое переменной PATH в Linux, выполните в терминале команду:
На экране появится перечень папок, разделённых двоеточием. Алгоритм поиска пути к требуемой программе при её запуске довольно прост. Сначала ОС ищет исполняемый файл с заданным именем в текущей папке. Если находит, запускает на выполнение, если нет, проверяет каталоги, перечисленные в переменной PATH, в установленном там порядке. Таким образом, добавив свои папки к содержимому этой переменной, вы добавляете новые места размещения исполняемых и связанных с ними файлов.
Для того, чтобы добавить новый путь к переменной PATH, можно воспользоваться командой export. Например, давайте добавим к значению переменной PATH папку/opt/local/bin. Для того, чтобы не перезаписать имеющееся значение переменной PATH новым, нужно именно добавить (дописать) это новое значение к уже имеющемуся, не забыв о разделителе-двоеточии:
Теперь мы можем убедиться, что в переменной PATH содержится также и имя этой, добавленной нами, папки:
Вы уже знаете как в Linux добавить имя требуемой папки в переменную PATH, но есть одна проблема — после перезагрузки компьютера или открытия нового сеанса терминала все изменения пропадут, ваша переменная PATH будет иметь то же значение, что и раньше. Для того, чтобы этого не произошло, нужно закрепить новое текущее значение переменной PATH в конфигурационном системном файле.
В ОС Ubuntu значение переменной PATH содержится в файле /etc/environment, в некоторых других дистрибутивах её также можно найти и в файле /etc/profile. Вы можете открыть файл /etc/environment и вручную дописать туда нужное значение:
sudo vi /etc/environment
Можно поступить и иначе. Содержимое файла .bashrc выполняется при каждом запуске оболочки Bash. Если добавить в конец файла команду export, то для каждой загружаемой оболочки будет автоматически выполняться добавление имени требуемой папки в переменную PATH, но только для текущего пользователя:
Выводы
В этой статье мы рассмотрели вопрос о том, зачем нужна переменная окружения PATH в Linux и как добавлять к её значению новые пути поиска исполняемых и связанных с ними файлов. Как видите, всё делается достаточно просто. Таким образом вы можете добавить столько папок для поиска и хранения исполняемых файлов, сколько вам требуется.
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How does the path environment variable work in Linux?
I’m confused how the PATH environment variable works under Linux. I’m a Linux Mint 15 user.
First, I read about editing the /home/.bashrc file and doing a PATH=$PATH:/directory ,
but I also knew about some path stuff managed in /etc/bash.bashrc
and so any software installed in /usr/local/bin would be reachable from anywhere in the shell.
How does the path variable work under Linux and where should it be placed?
4 Answers 4
The basic concept to grasp here is that PATH can be defined in many places. As @demure explains in his answer, PATH=$PATH:/new/dir means add /new_dir to $PATH , it will not clear the original $PATH .
Now, one reason there are many files is intimately connected with the concept of login and non-login shells. See here for a nice summary. The following is from the bash man page (emphasis mine):
When bash is invoked as an interactive login shell, or as a non-interactive shell with the —login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for
/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The —noprofile option may be used when the shell is started to inhibit this behavior.
When you first log into your system, you start a login shell so bash will read the files listed above. Most distributions set a system-wide $PATH (which applies to all users) at /etc/profile and this is where you should make any changes that you want applied to all users. This is what I have on my Debian:
Once you have logged in, when you open a terminal you start an interactive, non-login shell. This is what man bash has to say about those:
So, those files are read every time you open a new terminal. Your filnal $PATH is the combination of the values in all files. In a typical situation, you log in using a graphical log in manager and start a new session. At this pòint your $PATH is whatever was defined in the various profile files. If you open a terminal, then you are in an interactive shell and the different bashrc files are read which may append things to the $PATH .
To summarize, all you really need to know is that you can make changes to your user’s $PATH by editing $HOME/.profile .
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