hacktricks/linux-hardening/linux-environment-variables.md
2024-07-18 22:49:07 +02:00

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# 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
```
## Common variables
From: [https://geek-university.com/linux/common-environment-variables/](https://geek-university.com/linux/common-environment-variables/)
* **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 users 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 users 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.
[**This is an example**](https://gist.github.com/carlospolop/43f7cd50f3deea972439af3222b68808)
Root:
![](<../.gitbook/assets/image (897).png>)
Regular user:
![](<../.gitbook/assets/image (740).png>)
One, two and three backgrounded jobs:
![](<../.gitbook/assets/image (145).png>)
One background job, one stopped and last command didn't finish correctly:
![](<../.gitbook/assets/image (715).png>)
**Try Hard Security Group**
<figure><img src="../.gitbook/assets/telegram-cloud-document-1-5159108904864449420.jpg" alt=""><figcaption></figcaption></figure>
{% embed url="https://discord.gg/tryhardsecurity" %}
{% hint style="success" %}
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<details>
<summary>Support HackTricks</summary>
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
</details>
{% endhint %}