IT Toolbox

Linux

Linux / Administration

Linux

Linux commands, diagnostics and resources for Debian, Ubuntu, Bash, systemd, SSH, files, networking, logs and backups.

DebianUbuntuBashsystemdSSHrsyncjournalctl

6BAOI modules

20selected resources

6definitions

Tools & diagnostics

Direct access to the most relevant BAOI modules for this technology.

Troubleshooting Linux / Debian Center

Linux/Debian diagnostic: systemd, boot, network, DNS, SSH, disk, apt/dpkg, memory, logs, permissions, NTP and system time and Docker.

Open → Resource List failed systemd services

Displays the currently systemd units in state.

Open → Resource Identify large folders under Linux

Classifies the main root files according to their size to find the source of saturation.

Open → Resource List listening ports on Linux

Displays the TCP and UDP listening as well as associated processes.

Open → Resource Show Linux disk space and filesystems

Displays volumes mounted with their size, space used, space available and occupancy rates.

Open → Resource IT Cheat Sheets

Cheat sheets imprimables pour PowerShell, DNS, AD, FortiGate, Linux et plus.

Dictionary

Essential concepts related to Linux.

Dictionary SSH Jump Host

A Linux mechanism from the kernel, systemd, filesystem, or identity-management stack.

View → Dictionary SSH Host Key

A Linux mechanism from the kernel, systemd, filesystem, or identity-management stack.

View → Dictionary SSH Forwarding

A Linux mechanism from the kernel, systemd, filesystem, or identity-management stack.

View → Dictionary SSH ControlMaster

A Linux mechanism from the kernel, systemd, filesystem, or identity-management stack.

View → Dictionary NSS Linux

A Linux mechanism from the kernel, systemd, filesystem, or identity-management stack.

View → Dictionary Kerberos Client Linux

A Linux mechanism from the kernel, systemd, filesystem, or identity-management stack.

Practical guides

Step-by-step tutorials and procedures.

Guide How to find what fills a Linux drive

It is necessary to distinguish space saturation, saturation in inodes and deleted files still open before cleaning a Linux server.

View → Guide How to check the disk space of, Linux server

Quickly display the use file systems on Linux.

View → Guide How to scan a systemd service that does not start

systemctl gives the immediate state of the service while journalctl often explains why the main process has stopped.

View → Guide How to diagnose a systemd timer

This BAOI guide provides a structured method for diagnosing a systemd timer without multiplying unnecessary changes.

View → Guide How to diagnose a Linux filesystem read-only

Reading-only editing can be a protective measure after a storage error or filesystem.

Troubleshooting

Related failures, errors and diagnostics.

Troubleshooting systemd timer does not trigger

A task planned via systemd does not run at the expected time.

View → Error code systemd — Start request repeated too quickly

systemd stopped restarting a service after several rapid failures.

View → Troubleshooting Docker volume fills the Linux disk

A container volume or log gradually consumes the entire filesystem.

View → Error code Linux — No spaceleft on device

The kernel or application can no longer write to the target filesystem.

View → Troubleshooting Filesystem Linux passed read-only

The file system is mounted read-only and the scripts fail.

Field procedures

Reusable intervention methods.

Procedure Set up a systemd timer

Replace a fragile cron job with a controlled systemd timer using a oneshot service, OnCalendar scheduling, Persistent behavior when appropriate, systemd-an…

View → Procedure Handle a saturated Linux filesystem without risky deletion

Recover space on a saturated Linux filesystem without deleting files blindly by checking blocks and inodes, du results, deleted-but-open files, journald an…

View → Procedure Set up an immutable backup repository

Deploy aFree Veeam Hardened Re Poker with dedicated Linux, single-use, immutability, role separation and removal/remediation test.

Cheat sheets

Quick references for operations.

Cheat sheet Linux — Essential commands

Linux field reference for system, processes, systemd, logs, storage, networking, DNS, firewall, accounts and SSH.

Related technologies

Continue exploring with complementary topics.

Technology IT Networking

Tools and methods for DNS, DHCP, VLANs, routing, Wi-Fi, switching, TCP/IP, latency, MTU and network diagnostics.

View → Technology Backup & Disaster Recovery

Backup, restore and disaster recovery resources for Veeam, Acronis, VSS, RPO, RTO, immutability, replication and restore testing.

View → Technology Cybersecurity

Defensive resources for phishing, ransomware, compromised accounts, MFA, hardening, firewalls, incidents and backup protection.

View → Technology Proxmox VE

Proxmox VE administration and troubleshooting for QEMU VMs, LXC containers, clusters, Ceph, storage, backups, migration and networking.

View → Technology SQL / Databases

SQL Server, MySQL, MariaDB and PostgreSQL administration and troubleshooting for connections, performance, blocking, backups, logs and storage.

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