# Linux – Administration

Overview of common Linux administration tasks. Focus on day‑to‑day system management rather than distribution‑specific tools.

For foundational concepts (kernel, filesystem, users, processes), see:

- [Linux / Basics](./Basics.md)

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## 1. User and Group Management

Linux uses users and groups to control access to files, processes, and services.

Typical administration tasks include:

- Creating and removing users.
- Adding users to groups (for example to grant `sudo` access).
- Locking or disabling accounts.

Key ideas:

- Each user has a numeric user ID (UID) and a primary group ID (GID).
- Additional group memberships are used to grant extra permissions (for example access to Docker or systemd‑journal).

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## 2. Privileged Access and sudo

Administrative operations are usually performed with elevated privileges.

Approaches:

- Direct `root` login (less common on modern systems for security reasons).
- Using `sudo` to run specific commands as `root`.

Principles:

- Only trusted users should have `sudo` rights.
- The set of allowed commands can be restricted via the sudoers configuration.

In practice, administration is often done as an unprivileged user with `sudo` used only when needed.

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## 3. Filesystem Permissions and Ownership

Correct file and directory permissions are central to system security and stability.

Key aspects:

- Ownership (user and group) defines who primarily controls a resource.
- Permission bits (read, write, execute) for user, group, and others control what can be done.
- Special bits (setuid, setgid, sticky) influence execution and inheritance in specific cases.

Administration tasks related to permissions include:

- Adjusting ownership for application data directories.
- Ensuring configuration files are restricted when they contain secrets.
- Verifying that log and temporary directories have appropriate access.

Additional reminders and command examples can be kept in:

- [Linux / Cheat Sheet](./CheatSheet.md)

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## 4. Services and systemd Units

On many modern Linux distributions, **systemd** is used as the init system and service manager.

Concepts:

- A **unit** defines how a service, mount, timer, or other resource is started and managed.
- Service units (for example `ssh.service`, `docker.service`) describe how to start and stop daemons.
- Targets group units to represent boot states (for example `multi-user.target`).

Typical administration actions:

- Starting, stopping, and restarting services.
- Enabling or disabling services at boot.
- Checking service status and logs.

Systemd units are usually stored under `/lib/systemd/system` or `/etc/systemd/system`. Local overrides can be created without modifying vendor files.

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## 5. Logs and Troubleshooting

System logs are essential for diagnosing issues.

On systemd‑based systems, the journal stores logs from the kernel and many services.

Common tasks:

- Viewing recent logs for a specific service.
- Filtering logs by priority or time range.
- Inspecting boot logs to understand startup problems.

In addition to the journal, many services also write to files under `/var/log`. Knowing where a service writes its logs is an important part of administration.

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## 6. Software Installation and Updates

Package management is used to install, update, and remove software.

Administration concerns:

- Keeping the system reasonably up to date for security fixes.
- Avoiding unnecessary packages on minimal or security‑sensitive systems.
- Understanding which repositories are enabled.

The concrete commands differ per distribution (for example `apt` vs `dnf`), but the underlying tasks are similar.

Distribution‑specific notes and examples can be recorded in a dedicated cheat sheet or in project‑specific documentation.

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## 7. Scheduled Tasks and Automation

Linux systems provide several mechanisms for scheduled or automated tasks.

Common options:

- `cron` jobs for periodic execution.
- systemd timers for more structured scheduling tied to units.

These mechanisms are used for activities such as log rotation, backups, or periodic health checks.

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## 8. Backup and Recovery Considerations

From an administrative perspective, backup and recovery planning includes:

- Identifying which directories and data must be backed up.
- Choosing backup tools and storage locations.
- Testing restore procedures.

Details are often project‑specific and can be documented alongside the systems that depend on them (for example in a home‑server or application‑specific section).

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## 9. Relation to Other Documents

- [Linux / Cheat Sheet](./CheatSheet.md)