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====== VEOS Administrator Guide ======

**VEOS** is a multi-user Linux-based operating system for managing telecom services.\\  
This guide contains basic operating principles, administration commands, and configuration examples.

**Key VEOS features:**
  * Compatibility with standard Linux commands and utilities
  * Management through the **bash** command shell (default)
  * File system compliant with the **FHS** standard
  * Initialization through **systemd**
  * Access control based on users and groups

----

===== 1. Process management in VEOS =====

A **process** is a program loaded into the server memory and currently being executed.  
Processes are divided into two types:

^ Process type ^ Description ^ Examples ^
| **System** | Ensure OS operation and services | ''%%systemd%%'', ''%%kernel%%'', ''%%sshd%%'' |
| **User** | Started on behalf of a user | ''%%bash%%'', ''%%ls%%'', ''%%cat%%'' |

**Commands for process management:**

^ Action ^ Command ^ Note ^
| View all processes | ''%%ps aux%%'' | Shows PID, CPU, memory |
| Process tree | ''%%pstree%%'' | Parent-child hierarchy |
| Run in background | ''%%command &%%'' | Add ''%%&%%'' at the end |
| Stop a process by PID | ''%%kill <PID>%%'' | Use ''%%kill -9 <PID>%%'' for forced termination |

== Background mode ==
A process can run without user interaction (in the background). Use ''%%&%%'' to move it to the background.  
If the process requires input, it will be stopped by the kernel until returned to normal mode.

== Example ==
<code bash>
# Run a script in the background
./backup.sh &

# View background jobs in the current session
jobs
</code>

----

===== 2. Working with the file system =====

VEOS uses a **hierarchical Linux file system** — a single tree starting from the root ''%%/%%''.  
Different partitions and devices are mounted into directories (mount points).

=== 2.1. Root directory structure ===

Most important directories:

^ Directory ^ Contents ^
| ''%%/bin%%'' | Command shells and basic utilities |
| ''%%/boot%%'' | System kernel and bootloader |
| ''%%/dev%%'' | Device pseudo-files (created by ''%%udev%%'') |
| ''%%/etc%%'' | Configuration files |
| ''%%/home%%'' | User home directories |
| ''%%/opt/vasexperts%%'' | VAS Experts products |
| ''%%/proc%%'' | Virtual FS with process information |
| ''%%/root%%'' | Administrator home directory |
| ''%%/sbin%%'' | System administration utilities |
| ''%%/tmp%%'' | Temporary files |
| ''%%/usr%%'' | User applications and libraries |
| ''%%/var%%'' | Variable data (logs, queues, cache) |

=== 2.2. Navigating the directory tree ===

^ Command ^ Action ^
| ''%%pwd%%'' | Show the current directory |
| ''%%ls [directory]%%'' | List files (use the ''%%-l%%'' option for detailed output) |
| ''%%cd <directory>%%'' | Change directory |
| ''%%cd ..%%'' | Move one level up |
| ''%%cd /%%'' | Go to the root directory |

<note important>
**Important:** File and directory names are **case-sensitive** — ''%%test.txt%%'' and ''%%TEST.TXT%%'' are different files.
</note>

=== 2.3. Disk and partition names ===

Devices are displayed in ''%%/dev/%%'':

^ Device ^ Name ^
| First disk | ''%%/dev/sda%%'' |
| Second disk | ''%%/dev/sdb%%'' |
| Disk partition | ''%%/dev/sda1%%'', ''%%/dev/sda2%%'', … |

**Minimum partitions required for VEOS installation:**
  * Root partition ''%%/%%''
  * ''%%swap%%'' partition (recommended size — from one to two times the amount of RAM)
  * Optional: separate partitions for ''%%/home%%'', ''%%/var%%'', ''%%/usr%%''

----

===== 3. The bash shell =====

**Bash** (Bourne Again Shell) is the primary shell in VEOS.

=== 3.1. Useful keyboard shortcuts ===

^ Shortcut ^ Action ^
| ''%%Ctrl+A%%'' | Move to the beginning of the line |
| ''%%Ctrl+U%%'' | Delete the entire line |
| ''%%Ctrl+C%%'' | Stop the current task |
| ''%%Ctrl+R%%'' | Search command history |
| ''%%Tab%%'' | Auto-complete command/file name |

=== 3.2. Command history ===

^ Command ^ Action ^
| ''%%history%%'' | Show the list of recent commands |
| ''%%!!%%'' | Repeat the last command |
| ''%%!<number>%%'' | Execute the command with the specified number |

=== 3.3. Grouping and chaining commands ===

^ Operator ^ Purpose ^ Example ^
| ''%%;%%'' | Sequential execution | ''%%cd /tmp; ls -la%%'' |
| ''%%\|%%'' (pipe) | Pass stdout of the first command as stdin to the second | ''%%ls \| grep .txt%%'' |
| ''%%>%%'' | Redirect stdout to a file (overwrite) | ''%%echo hello > file.txt%%'' |
| ''%%>>%%'' | Append stdout to the end of a file | ''%%echo world >> file.txt%%'' |
| ''%%<%%'' | Use a file as stdin | ''%%sort < file.txt%%'' |

**Example of a pipe with sorting:**
<code bash>
# Sort the list of files in /etc in reverse order
ls -la /etc | sort -r
</code>

----

===== 4. User and permission management =====

Users are identified by **UID** (numeric identifier), groups by **GID**.

=== 4.1. Basic commands ===

^ Action ^ Command ^ Note ^
| View information about the current user | ''%%id%%'' | Shows UID, GID, groups |
| Change password | ''%%passwd%%'' | The current user changes their own password |
| Change another user's password | ''%%passwd <login>%%'' | Root only |
| Add a user | ''%%useradd <login>%%'' | Then set a password using ''%%passwd%%'' |
| Modify user parameters | ''%%usermod <options> <login>%%'' | For example, ''%%-G wheel%%'' |
| Delete a user | ''%%userdel <login>%%'' | Add ''%%-r%%'' to remove the home directory |

=== 4.2. Groups and permissions ===

Each user belongs to at least one group (with the same name).\\
Additional groups are assigned using ''%%usermod -G%%''.

**Example of adding a user to the ''%%wheel%%'' group (for ''%%sudo%%'' access):**
<code bash>
usermod -G wheel test
</code>

**View user groups:**
<code bash>
id test
</code>

<note important>
**Attention:** Most privileged utilities in VEOS use the **SGID** bit rather than SUID. Be careful when changing group permissions on system directories.
</note>

----

===== 5. Superuser mode (root) =====

The **superuser (root)** has unrestricted access to all files and processes.

=== 5.1. The ''su'' command ===

^ Command ^ Result ^
| ''%%su -%%'' | Full login as root (with root environment) |
| ''%%su%%'' | Only changes the user, keeps the current environment (not recommended) |

**Why ''%%su -%%'' is important:**\\  
Without the hyphen, the ''%%$PATH%%'' and ''%%$HOME%%'' variables remain from the regular user, and commands from ''%%/sbin%%'' and ''%%/usr/sbin%%'' may be unavailable.

=== 5.2. The ''sudo'' command ===

Allows executing individual commands as root without fully switching users.\\  
To use ''%%sudo%%'', the user must belong to the ''%%wheel%%'' group.

----

===== 6. systemd initialization system =====

**systemd** is the primary initialization system in VEOS. It starts services in parallel and tracks dependencies.

=== 6.1. Basic service management commands ===

^ Action ^ Command (systemd) ^ Sysvinit equivalent ^
| Start a service | ''%%systemctl start <service>%%'' | ''%%service <service> start%%'' |
| Stop a service | ''%%systemctl stop <service>%%'' | ''%%service <service> stop%%'' |
| Restart a service | ''%%systemctl restart <service>%%'' | ''%%service <service> restart%%'' |
| View service status | ''%%systemctl status <service>%%'' | ''%%service <service> status%%'' |
| Enable autostart | ''%%systemctl enable <service>%%'' | ''%%chkconfig <service> on%%'' |
| Disable autostart | ''%%systemctl disable <service>%%'' | ''%%chkconfig <service> off%%'' |

**Example for the ''%%fastdpi%%'' service:**
<code bash>
systemctl start fastdpi.service
systemctl status fastdpi.service
systemctl enable fastdpi.service
</code>

=== 6.2. Viewing logs (journal) ===

^ Command ^ Action ^
| ''%%journalctl%%'' | Show the full system journal |
| ''%%journalctl -b%%'' | Show logs only from the current boot |
| ''%%journalctl -f%%'' | Follow new messages (similar to ''%%tail -f%%'') |
| ''%%journalctl -u <service>%%'' | Logs for a specific service |

**Example:**
<code bash>
journalctl -u fastdpi.service -b
</code>

----

===== 7. Frequently asked questions (FAQ) =====

**Question:** Which command shell is used in VEOS by default?\\  
**Answer:** **bash**. You can check it using ''%%echo $SHELL%%''.

**Question:** How do I obtain root privileges with the full environment?\\  
**Answer:** Run ''%%su -%%''. Make sure to include the hyphen.

**Question:** What is ''%%systemd%%'' and how is it better than ''%%sysvinit%%''?\\  
**Answer:** ''%%systemd%%'' starts services in parallel, which speeds up boot time, and it does not stop the entire process if one service hangs.

**Question:** Which two hard disk partitions are required for VEOS?\\  
**Answer:** The root partition ''%%/%%'' and the ''%%swap%%'' partition.

**Question:** How do I view logs for a specific service?\\  
**Answer:** Use ''%%journalctl -u service_name.service%%''.

**Question:** Can ''%%sudo%%'' be used in VEOS?\\  
**Answer:** Yes, if the user is added to the ''%%wheel%%'' group. Example: ''%%sudo systemctl restart fastdpi%%''.

----

<details>
<summary>📌 Technical document information</summary>

**Document last reviewed:** 2026-05-12\\  
**Applicable VEOS version:** 8.6 and later\\  
**Author:** VAS Experts

</details>