Process States
In ps output, this single letter represents a process that is actively running on the CPU or waiting in the run queue for its turn.
What is R (Running / Runnable)?
This is the default signal sent when the kill command is run without specifying a signal
What is SIGTERM?
Most standard system log files on a Linux system live inside this directory.
What is /var/log?
This is the first process started by the Linux kernel at boot, the parent of all user-space processes, and always has PID 1.
What is init or systemd?
This command provides a snapshot of currently running processes and, without flags, shows only those in the current terminal.
What is ps?
This interruptible sleep state describes a process waiting for user input.
What is S?
This signal forces immediate termination and cannot be blocked, caught, or ignored.
What is SIGKILL?
This command queries the systemd journal, letting you filter logs by service, time range, or boot session.
What is journalctl?
This simple shell command prints the version string of the currently running Linux kernel.
What is uname -r?
This command provides a real-time, continuously updating display of running processes, typically sorted by CPU usage.
What is top?
This uninterruptible sleep state occurs when a process is waiting on hardware I/O and cannot be killed.
What is D?
This signal is automatically sent to a parent process when one of its child processes stops or terminates.
What is SIGCHLD?
This logging daemon directs system messages to various destinations based on facility and severity levels (HINT: system log messages to files, consoles, or remote servers).
What is rsyslog?
This privileged execution mode allows the kernel full access to hardware and system resources.
What is kernel mode?
This command sends a signal to all processes matching a given name, without needing a PID.
What is killall?
A process that has finished execution but remains in the process table until its parent acknowledges it is known by this name.
What is a Z (Zombie process)?
Pressing Ctrl+Z in the terminal sends this signal to the foreground process, suspending it.
What is SIGTSTP?
This command reads the kernel ring buffer and is commonly used to diagnose hardware issues and review boot messages.
What is dmesg?
his kernel component determines which process gets CPU time next, using algorithms such as the Completely Fair Scheduler.
What is the process scheduler?
This ps flag combination lists every process on the system with full detail, including background daemons with no terminal.
What is ps aux?
This is the key behavioral difference between a process by SIGSTOP versus SIGTSTP
SIGSTOP cannot be blocked or ignored; SIGTSTP can be caught or handled by the process.
This signal resumes a stopped process, allowing it to continue execution.
What is SIGCONT?
This utility automatically rotates, compresses, and archives log files on a configured schedule.
What is logrotate?
These kernel components can be dynamically loaded to extend system functionality without restarting the system.
What is Loadable Kernel Modules?
This command returns the PID of a running process by name and is commonly used in shell scripts to check if a service is active.
What is pgrep?