Linux Foundation Certified System Administrator (LFCS): key terms

Flashcards for this exam Linux Foundation Certified System Administrator (LFCS) guide

• /dev DirectoryThe Linux directory containing device files that represent hardware and pseudo-devices, such as disks, terminals and /dev/null.Foundational
• /etc DirectoryThe Linux directory holding host-specific, system-wide configuration files such as passwd, fstab, hosts and service configs.Foundational
• /etc/fstabThe Linux file that lists filesystems to mount automatically at boot, with their devices, mount points, types and options.Foundational
• /etc/groupThe Linux file that defines local groups, their GIDs and their supplementary members.Foundational
• /etc/hostsA local Linux file mapping hostnames to IP addresses, checked before or instead of DNS according to nsswitch.conf.Foundational
• /etc/passwdThe world-readable Linux file listing local user accounts with UID, GID, home directory and login shell.Foundational
• /etc/resolv.confThe Linux resolver configuration file listing DNS nameservers and search domains.Foundational
• /etc/shadowThe root-only Linux file that stores hashed user passwords and password aging information.Foundational
• /etc/sudoersThe configuration file defining which users and groups may run which commands via sudo.Intermediate
• /proc Filesystem (procfs)A virtual filesystem generated by the kernel that exposes process and system information as files under /proc.Intermediate
• /sys Filesystem (sysfs)A virtual filesystem mounted at /sys that exposes kernel objects such as devices, drivers and buses in a structured hierarchy.Intermediate
• /var DirectoryThe Linux directory for variable data that changes during operation, including logs, spool files, caches and databases.Foundational
• Ansible PlaybookA YAML file containing one or more plays that map groups of hosts to ordered tasks executed with Ansible modules.Foundational
• AppArmorA Linux mandatory access control module that confines programs using path-based profiles, default on Ubuntu and SUSE.Intermediate
• APTThe Advanced Package Tool, the high-level package manager for Debian, Ubuntu and related distributions.Foundational
• autofsA Linux service that mounts filesystems automatically on access and unmounts them after a period of inactivity.Advanced
• awkA Linux pattern-scanning and text-processing language that splits lines into fields for filtering and reporting.Intermediate
• BashThe Bourne Again Shell, the default command interpreter and scripting language on most Linux distributions.Foundational
• blkidA Linux command that displays block device attributes such as filesystem type, label and UUID.Foundational
• BtrfsA copy-on-write Linux filesystem with built-in snapshots, subvolumes, checksums, compression and multi-device support.Intermediate
• chageThe Linux command that views and sets password aging policy for a user account.Intermediate
• chattrA Linux command that sets extended filesystem attributes, such as immutable (+i) or append-only (+a), on files.Advanced
• chmodThe Linux command that changes file and directory permission bits using symbolic or octal notation.Foundational
• chownThe Linux command that changes the user and/or group owner of files and directories.Foundational
• chronyThe default NTP implementation on modern Linux that synchronizes the system clock with time servers.Intermediate
• cloud-initThe industry-standard tool for initializing cloud instances at first boot using user data.Intermediate
• Compiling Software from SourceBuilding a program from its source code, typically using configure, make and make install.Intermediate
• CronA time-based job scheduler and its five-field schedule syntax (minute, hour, day of month, month, day of week).Foundational
• crontabA per-user schedule table for cron jobs, and the command used to edit, list or remove it.Foundational
• DaemonA background process that runs without an interactive terminal, typically providing a system service.Foundational
• Device Mapper Multipath (DM-Multipath)A Linux feature that combines multiple I/O paths to a SAN LUN into one device for redundancy and load balancing.Advanced
• dfThe Linux disk free command that reports total, used and available space for each mounted filesystem.Foundational
• dmesgA Linux command that prints the kernel ring buffer containing hardware detection, driver and kernel messages.Foundational
• DNFThe default high-level package manager on RHEL, Fedora and derivatives, successor to YUM, resolving dependencies from repositories.Foundational
• dpkgThe low-level Debian package tool that installs, removes and queries .deb files without repository dependency resolution.Foundational
• duThe Linux disk usage command that totals space consumed by files and directories.Foundational
• Environment VariableA named value in a process environment that programs and shells read for configuration, such as PATH, HOME or LANG.Foundational
• Exit StatusThe numeric code a Linux command returns on completion, where 0 means success and non-zero indicates an error.Foundational
• ext4The fourth extended filesystem, a mature journaling filesystem that is the default on many Debian and Ubuntu Linux systems.Foundational
• fdiskAn interactive Linux command-line utility for creating, deleting and listing disk partitions on MBR and GPT disks.Foundational
• Filesystem Hierarchy Standard (FHS)The standard that defines the directory layout and purpose of top-level directories on Linux and Unix-like systems.Foundational
• findA Linux command that searches directory trees for files matching criteria such as name, type, size, age, owner or permissions.Foundational
• firewalldThe dynamic host firewall manager on RHEL and Fedora that uses zones and services on top of nftables.Intermediate
• firewalld ZoneA named firewalld trust level, such as public, internal or trusted, that applies a rule set to interfaces or source addresses.Intermediate
• fsckThe Linux filesystem consistency check and repair utility, run on unmounted filesystems.Foundational
• grepA Linux command that searches text for lines matching a pattern or regular expression.Foundational
• GRUB 2The GRand Unified Bootloader version 2, the standard Linux boot loader that loads the kernel and initramfs.Intermediate
• GUID Partition Table (GPT)A modern disk partitioning scheme, part of the UEFI specification, supporting disks over 2 TiB and up to 128 partitions by default.Foundational
• Hard LinkAn additional directory entry that points to the same inode as an existing file, making both names equal references to the same data.Intermediate
• hostnamectlA systemd utility that views and sets the system hostname and related host metadata.Foundational
• initramfsAn initial RAM filesystem loaded by the boot loader that contains drivers and tools needed to mount the real root filesystem.Advanced
• InodeA filesystem data structure storing a file's metadata (owner, permissions, timestamps, block pointers) but not its name.Intermediate
• iostatA Linux sysstat command that reports CPU and per-device I/O statistics such as IOPS, throughput, latency and utilization.Intermediate
• ipThe iproute2 Linux command for viewing and configuring addresses, links, routes and neighbors, replacing ifconfig and route.Foundational
• iptablesThe legacy Linux packet-filtering command that manages netfilter tables and chains such as INPUT, OUTPUT and FORWARD.Intermediate
• iSCSI InitiatorThe client side of an iSCSI connection, implemented in software or a hardware adapter, that sends SCSI commands to a target.Intermediate
• iSCSI Qualified Name (IQN)The globally unique name format identifying iSCSI initiators and targets, based on a date and reversed domain name.Intermediate
• iSCSI TargetThe storage side of an iSCSI connection that presents LUNs to authorized initiators.Intermediate
• journalctlThe command for querying logs collected by systemd-journald, filtered by unit, time, priority or boot.Intermediate
• Journaling File SystemA filesystem that records pending changes in a journal before committing them, enabling fast and consistent recovery after a crash.Foundational
• Kernel ModuleA loadable piece of kernel code, typically a device driver, that can be inserted or removed without rebooting.Intermediate
• Kernel PanicA fatal error from which the Linux kernel cannot safely recover, causing the system to halt or reboot.Intermediate
• Kernel-based Virtual Machine (KVM)A Type 1 hypervisor built into the Linux kernel that turns Linux into a host for virtual machines.Intermediate
• KickstartRed Hat's automated installation method that uses a configuration file to answer all installer prompts.Intermediate
• libvirtAn open-source API, daemon and toolkit for managing virtualization platforms such as KVM/QEMU.Intermediate
• Linux Boot ProcessThe sequence of firmware, boot loader, kernel, initramfs and init system that brings a Linux host to an operational state.Intermediate
• Linux File PermissionsThe read, write and execute (rwx) access bits that Linux assigns separately to a file's owner, group and others.Foundational
• Linux KernelThe core of the Linux operating system that manages CPU scheduling, memory, devices, filesystems and networking.Foundational
• Linux SignalsSoftware interrupts sent to processes to request actions such as terminate, reload or stop, using commands like kill.Foundational
• Load AverageThe average number of processes running or waiting for CPU or uninterruptible I/O over 1, 5 and 15 minutes on Linux.Intermediate
• Logical Volume (LV)In LVM, a virtual block device allocated from a volume group that is formatted and mounted like a partition.Intermediate
• Logical Volume Manager (LVM)A Linux storage layer that pools physical disks into volume groups and carves flexible, resizable logical volumes from them.Intermediate
• logrotateA Linux utility that rotates, compresses and removes old log files on a schedule to control disk usage.Intermediate
• lsblkA Linux command that lists block devices in a tree, showing disks, partitions, LVM volumes and their mount points.Foundational
• lsofA Linux command that lists open files and the processes using them, including network sockets.Intermediate
• LVM SnapshotA point-in-time copy of a logical volume that uses copy-on-write to record changes, commonly used for consistent backups.Advanced
• Master Boot Record (MBR)A legacy partitioning scheme storing the boot loader and partition table in the first 512-byte sector of a disk.Foundational
• mkfsThe Linux command family that creates (formats) a filesystem on a block device, such as mkfs.ext4 or mkfs.xfs.Foundational
• mountThe Linux command that attaches a filesystem on a device or network share to a directory in the file tree.Foundational
• Mount PointAn existing directory where a filesystem is attached so its contents become accessible at that path.Foundational
• Network BondingCombining multiple Linux network interfaces into one logical interface for redundancy or increased throughput.Intermediate
• Network File System (NFS)A file-sharing protocol common in Unix and Linux environments, using TCP and UDP port 2049.Intermediate
• NetworkManagerThe default Linux network configuration daemon, managed with nmcli, nmtui or GUI tools.Intermediate
• nftablesThe modern Linux netfilter framework and nft command that replace iptables, ip6tables, arptables and ebtables.Advanced
• Nice ValueA Linux process scheduling priority from -20 (highest priority) to 19 (lowest) that influences CPU time allocation.Intermediate
• Octal Permission NotationA numeric representation of Linux permissions where read=4, write=2 and execute=1 are summed per owner, group and others.Foundational
• ParavirtualizationAn approach in which the guest OS uses hypervisor-aware drivers or interfaces instead of emulated hardware, improving performance.Intermediate
• partedA GNU partition editor that manages MBR and GPT partition tables and can be scripted non-interactively.Intermediate
• PATH VariableThe environment variable listing directories the shell searches, in order, for executable commands.Foundational
• Physical Volume (PV)In LVM, a disk or partition initialized with pvcreate so it can contribute storage to a volume group.Intermediate
• PipeThe shell | operator that sends one command's standard output to another command's standard input.Foundational
• Pluggable Authentication Modules (PAM)A modular Linux framework that lets applications authenticate users through configurable stacks of modules.Advanced
• PodmanA daemonless, open-source container engine from Red Hat with a Docker-compatible CLI that supports rootless containers and pods.Intermediate
• POSIX Access Control List (ACL)Extended Linux permissions that grant specific users or groups access to a file beyond the single owner, group and others classes.Advanced
• Preboot Execution Environment (PXE)A standard that lets a computer boot from the network, using DHCP to find a boot server and TFTP to download a boot image.Intermediate
• Process ID (PID)A unique number the Linux kernel assigns to each running process.Foundational
• psA Linux command that reports a snapshot of current processes with details such as PID, user, CPU and memory usage.Foundational
• QEMUAn open-source machine emulator and virtualizer that provides device emulation for KVM virtual machines.Intermediate
• RedirectionShell syntax that sends a command's input or output to or from files instead of the terminal.Foundational
• restoreconAn SELinux command that resets file security contexts to the defaults defined in policy.Advanced
• Root AccountThe Linux superuser account with UID 0 that bypasses normal permission checks.Foundational
• Root DirectoryThe top-level directory of the Linux filesystem tree, written as a single forward slash (/), from which every other path descends.Foundational
• RPM Package ManagerThe low-level package format and tool used by Red Hat, Fedora, SUSE and related Linux distributions.Foundational
• rsyncA Linux file synchronization tool that efficiently copies only changed data, locally or over SSH.Intermediate
• rsyslogA widely used Linux syslog daemon that writes log messages to files and can forward them to remote log servers.Intermediate
• RunlevelA legacy SysV init operating mode (0-6) defining which services run; replaced by systemd targets on modern Linux.Foundational
• sarThe System Activity Reporter, a sysstat tool that collects and reports historical CPU, memory, disk and network performance data.Intermediate
• Security-Enhanced Linux (SELinux)A Linux kernel mandatory access control system that confines processes using security labels and policy.Intermediate
• sedThe Linux stream editor that transforms text non-interactively, most often for search-and-replace.Intermediate
• SELinux BooleanAn on/off SELinux policy switch that enables optional behaviors without writing custom policy.Advanced
• SELinux ContextThe security label (user:role:type:level) attached to every file, process and port that SELinux uses for access decisions.Advanced
• SELinux ModesThe three SELinux operating states: enforcing (blocks and logs), permissive (logs only) and disabled.Intermediate
• semanageThe SELinux policy management tool for persistently configuring file contexts, port labels, booleans and user mappings.Advanced
• Set Group ID (SGID)A special permission that runs a file with its group's privileges, or makes new files in a directory inherit the directory's group.Intermediate
• Set User ID (SUID)A special permission that makes an executable run with the privileges of the file's owner rather than the user running it.Intermediate
• ShebangThe #! line at the top of a script that specifies which interpreter should execute it.Foundational
• Shell ScriptA text file containing shell commands and control logic executed in sequence to automate administrative tasks.Intermediate
• Software RAIDRAID implemented by the operating system rather than a dedicated controller, such as Linux mdadm or Windows Storage Spaces.Intermediate
• Software RepositoryA server-hosted collection of signed software packages and metadata from which package managers install and update software.Foundational
• ssA Linux socket statistics command that shows listening ports and connections, replacing netstat.Foundational
• SSH Key-Based AuthenticationLogging in to SSH servers with a public/private key pair instead of a password.Intermediate
• Standard StreamsThe three default data channels of a Linux process: standard input (0), standard output (1) and standard error (2).Foundational
• Sticky BitA directory permission that allows only a file's owner, the directory owner or root to delete or rename files within it.Intermediate
• StratisA Red Hat local storage management solution that builds pools and thin-provisioned XFS filesystems on top of block devices.Advanced
• suThe Linux substitute-user command that starts a shell as another user, root by default.Foundational
• sudoA Linux command that lets permitted users run commands as root or another user, with logging and fine-grained policy.Foundational
• Swap SpaceDisk space used as overflow for physical RAM, where the kernel moves inactive memory pages when memory is under pressure.Foundational
• Symbolic Link (symlink)A special file that contains a path to another file or directory, acting as a shortcut that can cross filesystems.Foundational
• sysctlA Linux command and configuration mechanism for reading and setting kernel parameters at runtime.Intermediate
• systemctlThe command-line tool for controlling systemd units and inspecting system state.Foundational
• systemdThe default Linux init system and service manager that runs as PID 1 and starts, stops and supervises services and other units.Foundational
• systemd TargetA systemd unit that groups other units to define a system state, replacing SysV runlevels.Intermediate
• systemd TimerA systemd unit that activates another unit on a calendar schedule or after a time interval, as an alternative to cron.Intermediate
• systemd Unit FileA configuration file describing a systemd-managed resource, such as a .service, .socket, .timer, .mount or .target unit.Intermediate
• tarThe Linux tape archive utility that bundles files and directories into a single archive, optionally compressed.Foundational
• tmpfsA Linux filesystem that stores files in virtual memory (RAM and swap), so its contents vanish at reboot.Intermediate
• topAn interactive Linux utility that continuously displays processes, CPU, memory and load average.Foundational
• tunedA Linux daemon that applies performance profiles tuning CPU, disk and network settings for a workload.Intermediate
• ulimitA shell built-in that views or sets per-process resource limits such as open files and processes.Intermediate
• umaskA per-process mask that removes permission bits from the defaults when new files and directories are created.Intermediate
• Unified Extensible Firmware Interface (UEFI)Modern system firmware that replaces legacy BIOS, supporting GPT boot disks, Secure Boot and a pre-boot environment.Foundational
• useraddThe low-level Linux command that creates a local user account and optionally its home directory.Foundational
• usermodThe Linux command that modifies an existing user account, such as groups, shell, home or lock status.Foundational
• VimA ubiquitous modal text editor on Linux, an improved version of vi, used for editing configuration files.Foundational
• virshThe libvirt command-line tool for managing KVM virtual machines, networks and storage pools.Intermediate
• Virtual Data Optimizer (VDO)A Linux device-mapper layer providing inline deduplication, compression and thin provisioning for block storage.Advanced
• vmstatA Linux command reporting virtual memory, process, CPU, paging and I/O statistics at intervals.Intermediate
• Volume Group (VG)In LVM, a pool of storage built from one or more physical volumes from which logical volumes are allocated.Intermediate
• XFSA high-performance 64-bit journaling filesystem and the default filesystem in Red Hat Enterprise Linux.Intermediate
• ZFSA combined filesystem and volume manager offering pooled storage, copy-on-write, end-to-end checksums, snapshots and software RAID-Z.Advanced
• Zombie ProcessA process that has exited but whose entry remains in the process table because its parent has not collected its exit status.Intermediate