LPIC-1 102-500 key terms

The first line of a script, written as #! followed by an interpreter path, which tells the kernel which program should execute the file when it is run directly.

A value passed to a shell script or function and referenced by number, such as $1 or $2, with $0 holding the script name and $# counting how many were supplied.

A shell variable maintained automatically, such as $?, $$, $! or $*, that reports information about the running shell or the most recent command rather than user data.

The numeric value a command returns to its parent when it finishes; zero conventionally means success and any nonzero value indicates some kind of failure or special condition.

A shell builtin, also written as brackets, that evaluates file, string and numeric conditions and returns an exit status used by if and while statements.

A shell token such as && or || that chains commands based on exit status, running the next command only when the previous one succeeded or only when it failed.

A shell feature written with backticks or $(...) that runs a command and replaces the expression with its standard output, often to assign a result to a variable.

The use of single quotes, double quotes or backslashes to control how the shell interprets characters, preventing unwanted word splitting, globbing or variable expansion.

The process by which the shell replaces a name such as $HOME with its stored value before running a command, optionally modified by braces or parameter operators.

A name-value pair exported from a shell to the processes it starts, commonly used to configure programs through settings like PATH, HOME and LANG.

A startup file such as /etc/profile or ~/.bash_profile that a login shell reads to set environment variables, aliases and other session defaults.

A shell shortcut that maps a short name to a longer command string, defined with the alias builtin and typically stored in a user's shell startup files.

A named block of shell commands defined inside a script or interactive session that can be called repeatedly and receives its own positional parameters.

A shell construct such as for, while or until that repeats a block of commands, often iterating over a list of words or over lines read from input.

A shell construct that compares one value against several patterns and runs the commands belonging to the first pattern that matches, ending with esac.

A daemon that runs scheduled commands at fixed times, reading per-user crontabs and system files that define minutes, hours, days and months for each job.

Both the file format listing scheduled jobs and the command used to edit, list or remove a user's cron table, typically with the -e, -l and -r options.

A systemd unit ending in .timer that triggers another unit on a calendar or monotonic schedule, offering logging and dependency handling beyond plain cron.

A configuration file describing a resource systemd manages, identified by a suffix such as .service, .socket, .mount or .target that states its type.

The binary, structured log maintained by systemd-journald and queried with journalctl, storing messages from the kernel, services and other sources with metadata.

A logging daemon that receives messages and writes them to text files according to rules in /etc/rsyslog.conf, using facilities and priorities to select destinations.

The practice of periodically renaming, compressing and deleting old log files so that disk space is bounded, usually managed by the logrotate utility and its configuration files.

A regional offset from UTC used to display local time, configured system-wide through /etc/localtime or the timedatectl command on systemd systems.

A protocol for synchronizing computer clocks with reference time servers, implemented on Linux by daemons such as chronyd or by the systemd-timesyncd service.

An entry in /etc/passwd that gives a login name, numeric user ID, home directory and default shell, paired with a password hash stored in /etc/shadow.

A named collection of user accounts defined in /etc/group, used to grant shared access to files; each user also has one primary group for new files.

A program that lets permitted users run commands as another account, usually root, according to rules in /etc/sudoers and logging each invocation.

Policies that force or limit password changes, stored in /etc/shadow and managed with chage or passwd options such as minimum age, maximum age and expiry warnings.

Pluggable Authentication Modules, a framework of stacked shared libraries configured under /etc/pam.d that controls how services authenticate users and enforce account rules.

The read, write and execute rights granted to a file's owner, its group and all other users, shown by ls -l and changed with chmod.

A value that masks permission bits when new files and directories are created, subtracting from the default modes of 666 and 777 respectively.

The setuid, setgid and sticky flags, shown as s, s and t in permission listings, which alter execution identity, group inheritance or deletion rights.

An access control list that grants permissions to individual users or groups beyond the traditional owner-group-other model, managed with getfacl and setfacl.

A public and private cryptographic key pair used for passwordless SSH authentication, with the public half stored in a remote account's authorized_keys file.

The sshd service that accepts incoming secure shell connections, configured in /etc/ssh/sshd_config with options controlling ports, authentication methods and access restrictions.

A set of rules that filter network traffic entering or leaving a host, implemented on Linux by tools such as nftables or iptables and their front ends.

A logical or physical endpoint for network traffic, named like eth0 or wlan0, whose addresses and state are viewed with ip addr and configured in distribution-specific files.

A numeric label assigned to an interface for sending and receiving packets, written in IPv4 dotted-decimal or IPv6 hexadecimal notation and paired with a prefix length.

The kernel's list of rules deciding which interface and gateway a packet should use for a given destination, inspected with ip route or the route command.

The component that translates host names into IP addresses, configured through /etc/resolv.conf or systemd-resolved and queried with tools such as dig or host.

A service that presents a graphical login screen and starts a user's desktop session after authentication, examples being GDM, LightDM and SDDM.

The traditional Unix display service that manages screens, keyboards and pointers and lets client applications draw windows, usually configured through files in /etc/X11.

A newer display protocol in which a compositor directly manages input, output and window drawing, replacing the separate X server architecture on many modern desktops.

A coordinated collection of programs providing a window manager, panels, settings and utilities, such as GNOME, KDE Plasma or Xfce, that forms a complete user interface.

An option that adapts the desktop for users with disabilities, for example screen magnification, on-screen keyboards, sticky keys or high-contrast themes.