Linux - Reading summaries Flashcards
systemd
Utility for activating system resources, server daemons, and other processes at boot time and on a running system.
systemctl start [unit]
Start a service or other systemd unit.
systemctl stop [unit]
Stop a service or other systemd unit.
systemctl reload [unit]
Reload configuration of a service or other systemd unit.
systemctl enable [unit]
Enable a service or other systemd unit to start automatically at boot time.
systemctl disable [unit]
Disable a service or other systemd unit from starting automatically at boot time.
systemctl status [unit]
Check the status of a service or other systemd unit.
systemctl list-dependencies [unit]
List all service units that a specific service unit depends on.
systemctl mask [unit]
Prevent a service unit from running, even to satisfy dependencies.
Service units
Managed by systemd to control individual services.
Socket units
Managed by systemd to control socket-based activation of services.
Path units
Managed by systemd to activate services based on file system events.
File ownership permissions
Three categories: user, group, and other users. Most specific permission applies. User permissions override group permissions, and group permissions override other permissions.
ls -l option
Used with the ls command to expand the file listing to include both file permissions and ownership.
chmod command
Changes file permissions from the command line.
Methods of representing permissions
Two methods: symbolic or octal.
chown command
Changes file ownership. The -R option recursively changes the ownership of a directory tree.
umask command
Displays or sets the default file permissions for newly created files.
Default umask values for Bash
Defined in /etc/login.defs and might be affected by settings in /etc/profile, /etc/bashrc, files in /etc/profile.d, or user’s shell initialization files.
suid, sgid, and sticky bits
Special permissions providing additional access-related features to files.
Process
A running instance of an executable program, with states including running, sleeping, stopped, or zombie.
ps command
Lists processes running on the system.
Terminal Session
Each terminal has its own session, with a foreground process and independent background processes.
jobs command
Displays processes within a terminal session.
Signal
A software interrupt reporting events to an executing program.
kill command
Sends a signal to control processes.
pkill command
Sends a signal to control processes based on process names.
killall command
Sends a signal to control processes based on process names.
Load Average
An estimate of how busy the system is.
top command
Displays dynamic real-time information about running processes and system resource usage.
uptime command
Displays how long the system has been running and the average system load over different time intervals.
w command
Displays information about currently logged-in users and what they are doing, including load average.
systemd
Provides a method for activating system resources, server daemons, and other processes at boot time and on a running system.
systemctl start/stop/reload/enable/disable [service]
Commands used with systemctl to manage services, including starting, stopping, reloading, enabling, and disabling.
systemd utility
Used to manage service units, socket units, and path units.
systemctl status [unit]
Command used to determine the status of system daemons and network services started by the systemd utility.
systemctl list-dependencies [unit]
Command to list all service units that a specific service unit depends on.
Masking a service unit
systemd feature allowing a service unit to be masked so that it does not run, even to satisfy dependencies.
ssh command
Allows users to securely access remote systems using the SSH protocol.
Known Hosts files (~/.ssh/known_hosts and /etc/ssh/ssh_known_hosts)
Files where client systems store identities of remote servers.
SSH authentication types
Supports both password-based and key-based authentication methods.
ssh-keygen command
Generates an SSH key pair for authentication.
ssh-copy-id command
Exports the public key to remote systems for key-based authentication.
sshd service
Implements the SSH protocol on Red Hat Enterprise Linux systems.
/etc/ssh/sshd_config file
Configuration file for advanced SSH settings.
Recommended SSH configurations
Disable remote logins as root and require public key authentication instead of password-based authentication.
TCP/IP network model
A simplified, four-layered model describing how different protocols interoperate for sending traffic over the internet.
IPv4
The primary network protocol used on the internet today.
IPv6
Intended as a replacement for IPv4 network protocol.
Dual-stack mode
Red Hat Enterprise Linux operates using both IPv4 and IPv6 protocols simultaneously by default.
Network routes
Determine the correct network interface to send packets to a particular network.
NetworkManager daemon
Monitors and manages network configuration.
nmcli command-line tool
Configures network settings with the NetworkManager daemon.
Network configurations directory
In Red Hat Enterprise Linux 9, the default location is /etc/NetworkManager/system-connections.
System’s static hostname
Stored in the /etc/hostname file.
hostnamectl command
Modifies or views the status of the system’s hostname and related settings.
Red Hat Subscription Management
Provides tools for entitlements, updates, and tracking support contracts and subscriptions.
RPM packages
Software provided in RPM format for installation, upgrading, and uninstallation on the system.
rpm command
Can query local database for package information and install downloaded package files.
dnf utility
A powerful command-line tool for installing, updating, removing, and querying software packages.
Application Streams
Red Hat’s feature to provide a single repository hosting multiple versions of application packages and dependencies.
Daemon
A background process that runs continuously on a computer system, performing various tasks without direct user interaction
