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Abbreviations
Cheat sheets
- apt cheat sheet
- AWK cheat sheet
- curl cheat sheet
- dmidecode cheat sheet
- du cheat sheet
- find cheat sheet
- ip cheat sheet
- journalctl cheat sheet
- lsof cheat sheet
- run0 cheat sheet
- ss cheat sheet
- strace cheat sheet
- systemctl cheat sheet
- systemd cheat sheet
- tar cheat sheet
- tcpdump cheat sheet
Command-line
Data processing
Definitions
Glossary
Hardware
Kernel
Linux file systems
- File systems: Frequently Asked Questions
- How to compare two directories and find the differences
- How to find symbolic links that point to a directory
- How to find the biggest directories on disk
- How to find when the last modification happened in a directory
- How to find writable files
- How to securely delete a file and its contents
- How to see files great than a specific size
- How to see hidden files
- How to see inode usage
- How to see the creation date of a file
- How to see the size of a directory
- How to see used and free disk space
- How to find hard links or files that point to a specific file
- Linux file permissions
- Understanding the output of the stat command
Linux security frameworks
Networking
- Networking: Frequently Asked Questions
- How to see active connections and bandwidth usage on Linux
- How to see errors and dropped packets on a network interface on Linux
- How to see open ports on Linux
- How to see the default gateway on Linux
- How to see the IP address of your internet connection
- How to see the number of open connections on Linux
- How to see the the network IP address of your system
- How to see the TTL value of a DNS record
- How to see which DNS server is used
- How to see which process is using a port
- How to show network TCP statistics and counters
- Show to clear the DNS cache with systemd
Processes
- Kill a process that won't respond to CTRL+C
- Linux process signals and their meaning
- Processes: Frequently Asked Questions
- How to find all process IDs by its process name
- How to kill a running process by its name
- How to kill a zombie process
- How to see cgroup in ps output
- How to see the cgroup of a process
- How to show a running process name and its process ID (PID)
- How to stop all processes of a single user
- What is a zombie process?
Security concepts
Shell scripting
- Check if a directory or file exists
- Making scripts (more) secure and safe
- Prompt for user input in a shell script
- Strip one or more characters from a variable or output
Software
SSH
- Change SSH server port number
- Configure a SSH welcome message or banner
- SSH Configuration
- SSH escape sequences
- SSH: Frequently Asked Questions
- How to disable the SSH host key check?
- How to disable the usage of the SSH agent
- How to remove the passphrase from a SSH key
- How to see the available SSH keys in the OpenSSH authentication agent
- How to start the SSH agent?
- How to terminate a SSH connection that does not respond to CTRL+C
- What is SSH agent forwarding?
- What is the purpose of the SSH agent?
- Using SSH keys instead of passwords
System administration
- /etc/ssh/ssh_config
- /etc/ssh/sshd_config
- Commands
- Methods to find the Linux distribution and version
- System administration: Frequently Asked Questions
System performance
systemd
- Hardening profiles for systemd
- Run0: introduction and usage
- Systemd commands
- Systemd features to secure units and services
- systemd settings
- Settings for systemd units
- DeviceAllow setting
- DevicePolicy setting
- InaccessiblePaths setting
- MemoryDenyWriteExecute setting
- ProcSubset setting
- ProtectHome setting
- ProtectKernelLogs setting
- ProtectKernelModules setting
- ProtectProc setting
- ReadWritePaths setting
- RestrictAddressFamilies setting
- SocketBindAllow setting
- SocketBindDeny setting
- SystemCallFilter setting
- Settings for systemd units
- Systemd syscall filtering
- Systemd timers
- systemd units and their purpose
- Systemd: Frequently Asked Questions
- How to check if 'systemctl daemon-reload' is needed
- How to disable a systemd unit with systemctl
- How to disable the background color of run0
- How to limit the disk usage of the systemd journal
- How to override the settings of a systemd unit
- How to reload the systemd configuration
- How to see all active systemd units of one type
- How to see all masked units with systemctl
- How to see kernel messages with journalctl
- How to see logging for a specific unit or service
- How to see memory usage of a service with systemctl?
- How to see new log entries automatically with journalctl
- How to see only recent journal entries
- How to see only running services with systemctl
- How to see the active settings of a systemd unit
- How to see the available systemd unit types
- How to see the dependencies of a systemd unit
- How to see the last X lines with journalctl
- How to see the size of the systemd journal
- How to see the time synchronization details with timedatectl
- How to see which syscalls are part of a systemd syscall filter set
- How to show failed units with systemctl
- How to show the systemd machine ID
- How to start and enable a unit with systemctl
- How to use systemctl edit to change a service?
- What does systemctl daemon-reload do?
- What is a masked systemd unit?
- What is a systemd unit?
- What is systemd?
- What is the difference between systemctl disable and systemctl mask?
- Troubleshooting a failed systemd unit (with examples)
Web
- Adding the Expires header to improve caching static content in nginx
- Hardening nginx with systemd security features
- How to log only some requests to a log file in nginx
- How to see all virtual hosts in nginx
- Nginx security hardening guide
- Pre-compress static assets with Brotli and Gzip
- Test web server caching with curl