Linux Processes and Regular Expressions

Vocabulary practice flashcards covering Linux process management, job control, signals, system resources, and regular expressions.

Process

A program in execution on a Linux system; an active entity with system resources, PID, and memory variables, started via GUI or CLI.

systemd

The first process spawned at system boot (PID 1) that replaced init; it serves as the parent of all other processes and executes continuously until system shutdown.

fork()

The system call used by a parent process to clone itself and start a new child process with its own PID.

Daemon

A long-running, background Linux process that operates without user intervention, often initialized at boot time to manage system tasks like mail scanning and network filesystems.

Background Process

A process launched by appending an ampersand (&) to a command; it runs alongside other processes without interactive shell control or locking the command prompt.

jobs

A command that displays active, running, or stopped jobs running in the current shell session.

Ctrl-Z

The terminal key sequence used to suspend (pause or stop) a currently running foreground process.

fg

The command used to resume a stopped or background process in the foreground, specified by job number (e.g., fg 1).

bg

The command used to resume a suspended/stopped process to continue running in the background.

ps

Process Status; a command-line tool that displays a non-interactive snapshot of currently running processes.

ps -aux

A ps command option set displaying all active processes (a), in user-oriented format (u), including processes not attached to a terminal (x).

TTY

Teletypewriter; indicates the controlling terminal device associated with a process, displayed as a question mark (?) when running detached under a GUI.

Zombie Process

A defunct process that has finished execution and surrendered its resources, but remains in the process table with a PCB because its parent process has not yet reaped its exit status.

Orphan Process

A process whose parent process has terminated; it is adopted by PID 1 (systemd or init).

Core File

A memory image file left behind when a process terminates abnormally, used by developers for debugging.

SIGTERM (Signal 15)

The default termination signal sent by kill, requesting a process to shut down cleanly and allow cleanup operations before exiting.

SIGKILL (Signal 9)

A brute-force kill signal that immediately forces Linux to abort a process without allowing cleanup routines.

SIGHUP (Signal 1)

The hang-up signal that terminates communication when a line disconnects or restarts a process with its exact same PID.

killall

A command that sends termination signals to processes specified by their process name rather than PID.

top

An interactive command-line utility displaying real-time, continuously updating system resource utilization and active process metrics, refreshing every 3 seconds by default.

Niceness (NI)

A user-space process priority value ranging from -20 (highest priority) to +19 (lowest priority); higher niceness values yield CPU time to other processes.

renice

The Linux utility used to modify the priority (niceness value) of an already running process.

mpstat

A command that displays processor utilization statistics across all processors in a system.

pmap

A command used to view the memory map and allocated memory addresses of a process specified by PID.

systemctl emergency

A systemctl shutdown mode switching the machine to single-user (root) text-based mode without running services or mounted file systems, executing only systemd and a shell.

systemctl kexec

A reboot mode executed directly by the kernel that bypasses the hardware ROM BIOS POST initialization phase.

Regular Expression (regex)

A specialized text pattern string consisting of literals and metacharacters used for pattern matching, filtering, and text manipulation.

Literal Character

A character in a regular expression that must match itself precisely in string order, case, and character value.

Metacharacter

A special non-literal character within a regular expression that alters matching rules for preceding or following characters.

Escape Character ()

A metacharacter used before any of the 14 special regex characters to instruct the interpreter to treat the symbol as a literal string character.

grep

Global Regular Expression Print; a text search utility that prints each line in a file matching a specified expression.

egrep

Extended grep; a version of grep supporting extended regular expression metacharacters (+, ?, |, and grouping parentheses) without escaping.

Dot Metacharacter (.)

A regex metacharacter that matches any single character except a newline or line break.

Star Metacharacter (*)

A quantifier specifying that the preceding character or grouped token may appear zero or more times.

Plus Metacharacter (+)

An extended metacharacter specifying that the preceding token must appear one or more times.

Question Mark Metacharacter (?)

An extended metacharacter that makes the preceding character or group optional by matching it exactly 0 or 1 time.

grep -v

A grep option that inverts matching to select only lines that do not match the specified pattern.

grep -w

A grep option that restricts search results to lines where matches form whole words.

grep -o

A grep option that outputs only the exact matching text segments rather than the full line.

Character Class ([ ])

A regex bracket expression used to specify a list or range of characters, matching any single character contained within.

Negated Character Class ([^ ])

A character class beginning with a caret (^) that matches any single character not included within the brackets.

Curly Braces ({n,m})

A quantifier metacharacter defining repetition ranges, matching the preceding token at least n times and at most m times.

Caret Anchor (^)

A positional metacharacter that anchors a match to the beginning of a line.

Dollar Anchor ($)

A positional metacharacter that anchors a match to the end of a line.

Word Boundary (\b)

A positional regex anchor that matches the boundary point between a word character [a-zA-Z0-9_] and a non-word character.

Alternation (|)

An extended regex metacharacter representing logical OR, matching either the expression to its left or to its right.

[:alnum:]

A POSIX character class matching any alphanumeric character (letters in either case or digits 0-9).

[:space:]

A POSIX character class matching any whitespace character, including blank space, tab, and newline.

/usr/share/dict/words

The standard system dictionary file on Linux containing a newline-delimited list of words used for text processing and regex pattern matching.