# Linux Environment Variables
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## Global variables The global variables **will be** inherited by **child processes**. You can create a global variable for your current session doing: ```bash export MYGLOBAL="hello world" echo $MYGLOBAL #Prints: hello world ``` This variable will be accessible by your current sessions and its child processes. You can **remove** a variable doing: ```bash unset MYGLOBAL ``` ## Local variables The **local variables** can only be **accessed** by the **current shell/script**. ```bash LOCAL="my local" echo $LOCAL unset LOCAL ``` ## List current variables ```bash set env printenv cat /proc/$$/environ cat /proc/`python -c "import os; print(os.getppid())"`/environ ``` ## Persistent Environment variables #### **Files that affect behavior of every user:** * ***/etc/bash.bashrc***: This file is read whenever an interactive shell is started (normal terminal) and all the commands specified in here are executed. * ***/etc/profile and /etc/profile.d/\******:** This file is read every time a user logs in. Thus all the commands executed in here will execute only once at the time of user logging in. * \*\*Example: \*\* `/etc/profile.d/somescript.sh` ```bash #!/bin/bash TEST=$(cat /var/somefile) export $TEST ``` #### **Files that affect behavior for only a specific user:** * ***\~/.bashrc***: This file behaves the same way */etc/bash.bashrc* file works but it is executed only for a specific user. If you want to create an environment for yourself go ahead and modify or create this file in your home directory. * ***\~/.profile, \~/.bash\_profile, \~/.bash\_login*****:** These files are same as */etc/profile*. The difference comes in the way it is executed. This file is executed only when a user in whose home directory this file exists, logs in. **Extracted from:** [**here**](https://codeburst.io/linux-environment-variables-53cea0245dc9) **and** [**here**](https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html) ## Common variables From: * **DISPLAY** – the display used by **X**. This variable is usually set to **:0.0**, which means the first display on the current computer. * **EDITOR** – the user’s preferred text editor. * **HISTFILESIZE** – the maximum number of lines contained in the history file. * \*\*HISTSIZE - \*\*Number of lines added to the history file when the user finish his session * **HOME** – your home directory. * **HOSTNAME** – the hostname of the computer. * **LANG** – your current language. * **MAIL** – the location of the user’s mail spool. Usually **/var/spool/mail/USER**. * **MANPATH** – the list of directories to search for manual pages. * **OSTYPE** – the type of operating system. * **PS1** – the default prompt in bash. * \*\*PATH - \*\*stores the path of all the directories which holds binary files you want to execute just by specifying the name of the file and not by relative or absolute path. * **PWD** – the current working directory. * **SHELL** – the path to the current command shell (for example, **/bin/bash**). * **TERM** – the current terminal type (for example, **xterm**). * **TZ** – your time zone. * **USER** – your current username. ## Interesting variables for hacking ### **HISTFILESIZE** Change the **value of this variable to 0**, so when you **end your session** the **history file** (\~/.bash\_history) **will be deleted**. ```bash export HISTFILESIZE=0 ``` ### **HISTSIZE** Change the **value of this variable to 0**, so when you **end your session** any command will be added to the **history file** (\~/.bash\_history). ```bash export HISTSIZE=0 ``` ### http\_proxy & https\_proxy The processes will use the **proxy** declared here to connect to internet through **http or https**. ```bash export http_proxy="http://10.10.10.10:8080" export https_proxy="http://10.10.10.10:8080" ``` ### SSL\_CERT\_FILE & SSL\_CERT\_DIR The processes will trust the certificates indicated in **these env variables**. ```bash export SSL_CERT_FILE=/path/to/ca-bundle.pem export SSL_CERT_DIR=/path/to/ca-certificates ``` ### PS1 Change how your prompt looks. I have created [**this one**](https://gist.github.com/carlospolop/43f7cd50f3deea972439af3222b68808) (based on another, read the code). Root: ![](https://github.com/nirugima/hacktricks/blob/main/.gitbook/assets/image%20\(87\).png) Regular user: ![](https://github.com/nirugima/hacktricks/blob/main/.gitbook/assets/image%20\(88\).png) One, two and three backgrounded jobs: ![](https://github.com/nirugima/hacktricks/blob/main/.gitbook/assets/image%20\(89\).png) One background job, one stopped and last command didn't finish correctly: ![](https://github.com/nirugima/hacktricks/blob/main/.gitbook/assets/image%20\(90\).png)
πŸŽ™οΈ HackTricks LIVE Twitch Wednesdays 5.30pm (UTC) πŸŽ™οΈ - πŸŽ₯ Youtube πŸŽ₯ * Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)! * Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family) * Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com) * **Join the** [**πŸ’¬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.** * **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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