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Key Terms Flashcards

1
Q

shell

A

The environment from which commands can be executed. Bash is the default shell on Linux, but other shells exist as well.

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2
Q

Bash

A

The default shell that is used on Red Hat Enterprise Linux.

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3
Q

File descriptor

A

A pointer that is used by a Linux process to refer to files that are in use by the process.

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4
Q

Device file

A

A file that is created in the /dev directory and that is used to represent and interact with a device.

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5
Q

Login shell

A

The shell that is opened directly after a user has logged in.

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6
Q

Subshell

A

A shell that is started from another shell. Typically, a subshell is started by running a shell script.

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7
Q

Mount

A

A connection that is made between a device and a directory. To access files on specific storage devices, the storage device needs to be mounted on a directory. This sets up the specified directory as the access point to files on the storage device. Mounts are typically organized by the system administrator and are not visible to end users.

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8
Q

inode

A

inodes are structures that store metadata about files and directories, including: File permissions, Ownership, Size, Timestamps, Location of the data. Every Linux file has an inode, and the inode contains all properties of the file but not the filename.

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9
Q

Hard link

A

A name associated with an inode. Inodes are used to store Linux files. An inode contains the complete administration of the file, including the blocks in which the file is stored. A file that does not have at least one hard link is considered a deleted file. To increase file accessibility, more than one hard link can be created for an inode.

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10
Q

Symbolic (soft) link

A

A special type of file that contains a reference to another file or directory in the form of an absolute or relative path.

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11
Q

Filesystem Hierarchy Standard (FHS)

A

A standard that defines which Linux directories should be used for which purpose.

Read man 7 file-hierarchy for a specification of the FHS.

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12
Q

Regular expression

A

A search pattern that allows users to search text patterns in a flexible way. Not to be confused with shell metacharacters.

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13
Q

Line anchor

A

In regular expressions, a character that refers to a specific position in a line.

^ signifies start of line
$ signifies end of line

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14
Q

Wildcard

A

The * character, which in a shell environment refers to an unlimited number of any characters.

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15
Q

Console

A

In Linux, the primary terminal where a user works. It is also a specific device with the name /dev/console.

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16
Q

Terminal

A

Originally, the screen that was used by a user to type commands on. On modern Linux systems, pseudo terminals can be used as a replacement. A pseudo terminal offers a shell window from which users enter the commands that need to be executed.

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17
Q

Subshell

A

A shell that is started from another shell. Typically, a subshell is started by running a shell script.

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18
Q

Systemd

A

The service manager on RHEL 9. Systemd is the very first process that starts after the kernel has loaded, and it takes care of starting all other processes and services on a Linux system.

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19
Q

GECOS

A

A field in the /etc/passwd file that can be used to store personal data about a user on the Linux operating system. GECOS originally stood for General Electric Comprehensive Operating Supervisor.

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20
Q

Inheritance

A

In permission management, the situation where new files that are created in a directory inherit the permission settings from the parent directory.

This can be enforced by setting the SGID bit on a directory’s permissions.

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21
Q

Repository

A

An installation source that contains installable packages and an index that contains information about the installable packages so that the installation program dnf can compare the version of packages currently installed with the version of packages available in the repository.

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22
Q

Package

A

A bundle that is used to distribute software. A package typically contains a compressed archive of files and metadata that includes instructions on how to install those files.

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23
Q

Module (dnf)

A

A collection of software packages that can be managed as one entity and can contain different versions of a software solution.

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24
Q

Application Stream

A

A specific version of a dnf module that can be installed as such. They are often used by developers who need a specific version of software to build or run their applcations.

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25
Process
A task that is running on a Linux machine. Roughly, a process corresponds to a program, although one program can start multiple processes.
26
Thread
A thread is a subdivision of a process. Many processes are single threaded, which means that process is basically one entity that needs to be serviced. On a multicore or multi-CPU computer system, working with multithreaded processes makes sense. That way, the different cores can be used to handle the different threads, which allows a process to benefit from multicore or multithreaded environments.
27
Job
In a Linux shell, a task running in the current terminal. Jobs can be started in the foreground and in the background. Every job is also visible as a process.
28
Background process
A process that is running on a system without actively occupying a console. Processes can be started in the background by adding a & after the command that starts the process.
29
Zombie
A process that has lost contact with its parent and for that reason cannot be managed using regular tools.
30
Profile (tuned)
In 'tuned', a collection of performance settings that can easily be applied.
31
Systemd
The service manager on RHEL 9. Systemd is the very first process that starts after the kernel has loaded, and it takes care of starting all other processes and services on a Linux system.
32
Unit
An item that is managed by Systemd. Different types of units exist, including service, path, mount, and target units.
33
Target
In Systemd, a collection of unit files that can be managed together.
34
Want
An indication for a Systemd unit file that it is supposed to be started from a specific Systemd target.
35
Timer
A Systemd unit type that can be used as an alternative to cron jobs and run units at a specific time.
36
cron
A service that takes care of starting services repeatedly at specific times.
37
anacron
A service that ensures that vital cron jobs can be executed when the server is down at the moment that the job normally should be executed. Can be considered an extension to cron.
38
at
A service that can be used to schedule future jobs for one-time execution.
39
systemd-journald
The part of Systemd that takes care of logging information about events that have been happening. The introduction of journald ensures that information about all services can be logged, regardless of how the service itself is configured to deal with information that is to be logged.
40
rsyslogd
The generic daemon that logs messages.
41
journalctl
The command used to manage systemd-journald.
42
Log rotation
A service that ensures that log files cannot grow too big. Log files are monitored according to specific parameters, such as a maximum age or size. Once this parameter is reached, the log file will be closed and a new log file will be opened. Old log files are kept for a limited period and will be removed, often after only a couple of weeks.
43
Facility
In rsyslogd, the source where log information comes from. A strictly limited number of facilities have been defined in rsyslogd.
44
Priority (rsyslog)
Used to specify the severity of a logged event. Based on the severity, specific actions can be taken.
45
Destination
In rsyslog, the place where log messages should be sent by the logging system. Destinations are often files, but can also be input modules, output modules, users, or hosts.
46
Partition
A subdivision of a hard disk on which a file system can be created to mount it into the directory structure.
47
Master Boot Record (MBR)
On a BIOS system, the first 512 bytes on the primary hard disk. It contains a boot loader and a partition table that give access to the different partitions on the hard disk of that computer.
48
GUID Partition Table
A modern solution to store partitions on a hard disk, as opposed to the older MBR partition table. In GUID partitions, a total of 128 partitions can be created, and no difference exists between primary, extended, and logical partitions anymore.
49
Primary partition
In MBR, one of up to partitions that can be created in the Master Boot Record.
50
Extended partition
A solution to create more than four partitions on an MBR disk. On MBR disks, a maximum of four partitions can be stored in the partition table. To make it possible to go beyond that number, one of the four partitions can be created as an extended partition. Within an extended partition, logical partitions can be created, which will perform just like regular partitions, allowing system administrators to create more partitions.
51
Logical partition
A partition that is created in an extended partition.
52
Universally Unique ID (UUID)
An identification number consisting of a long random hexadecimal number that is globally unique.
53
fstab
A configuration file that is used on Linux to mount file systems automatically when the system starts.
54
Label
A name that can be assigned to a file system. Using labels can be a good idea, because once a label is assigned, it will never be changed, which guarantees that the file system can still be mounted, even if other parameters such as the device name have changed. However, UUIDs are considered safer than labels because the chance of having a duplicate label by accident is much higher than the chance of having a duplicate UUID.
55
Snapshot
A “photo” of the actual state of a file system.
56
Physical volume (PV)
The foundational building block of an LVM configuration. The physical volume typically corresponds to a partition or a complete disk device.
57
Volume group (VG)
The abstraction layer that in Logical Volume Manager is used to represent all available storage presented by physical volumes from which logical volumes can be created.
58
Physical extent
The physical building block that is used when creating LVM physical volumes. Typically, the size is multiple megabytes.
59
Logical volume (LV)
In LVM, the entity on which a file system is created. Logical volumes are often used on RHEL because they offer important advantages, such as the option to dynamically resize the logical volume and the file system that it hosts.
60
Device mapper
A service that is used by the Linux kernel to communicate with storage devices. Device mapper is used by LVM, multipath, and other devices, but not by regular hard disks. Device files that are created by device mapper can be found in the /dev/mapper directory.
61
Logical extent
The building block that is used in LVM to create logical volumes. It normally has a size of a few megabytes that corresponds to the size of the physical extents that are used.
62
Stratis
The new volume managing file system that was introduced in RHEL 8.
63
Kernel
The central component of the operating system. It manages I/O requests from software and translates them into data processing instructions for the hardware in the computer
64
Tainted kernel
A kernel in which unsupported kernel modules have been loaded.
65
/proc
A kernel interface that provides access to kernel information and kernel tunables. This interface is available through the /proc file system.
66
Dependency
Generally, a situation where one item needs another item. Dependencies occur on multiple levels in Linux. In RPM package management, a dependency is a software package that needs to be present for another package to be installed. In Systemd, a dependency is a Systemd unit that must be loaded before another unit can be loaded.
67
Boot loader
Program that is started as the very first thing while starting a computer and that takes care of loading the operating system kernel and initramfs.
68
GRUB 2
The boot loader that is installed on most systems that need to start Linux. GRUB 2 provides a boot prompt from which different kernel boot options can be entered, which is useful if you need to troubleshoot the boot procedure.
69
initramfs
The initial RAM file system. Contains drivers and other files that are needed in the first stages of booting a Linux system. On Red Hat Enterprise Linux, the initramfs is generated during installation and can be manually re-created using the dracut utility.
70
dracut
A utility used to generate the initramfs, an essential part of the Linux operating system that contains drivers and other vital files required to start a Linux system.
71
fork
A system call that starts a new process as a child of the current process. This is the default way commands are executed.
72
exec
A system call that replaces the current process with another one.
73
shebang
The characters used in a script to indicate which shell should be used for executing the code in the shell script. If no shebang is used, the script code will be interpreted by the parent shell, which may lead to errors in some cases. A shebang starts with a #, which is followed by a ! and the complete pathname of the shell, such as #!/bin/bash
74
Parent shell
The environment from which a shell script or program is started. Processes or child scripts will inherit settings from the parent shell.
75
Variable
A label that contains a specific value that can be changed dynamically. In scripting, variables are frequently used to allow the script to be flexible.
76
Passphrase
Basically a password, but is supposed to be longer and more secure than a password.
77
chroot
An environment where a part of the file system is presented as if it were the root of the file system. Chroot is used as a security feature that hides part of the operating system that is not required by specific services.
78
Virtual host
In the Apache web server, a collection of configuration settings that is used to address a web server. What makes it a virtual host is that one installation of the Apache web server can be configured with multiple virtual hosts, which allows administrators to run multiple websites on one Apache server.
79
SELinux Policy
The collection of rules that is used to define SELinux security.
80
Context
In SELinux, a label that is used to define the security attributes of users, processes, ports, and directories. These contexts are used in the SELinux policy to define security rules.
81
Enforcing
The SELinux mode where SELinux is fully operational and applies all restrictions that have been configured for a specific system.
82
Permissive
The SELinux mode where nothing is blocked but everything is logged in the audit log. This mode is typically used for troubleshooting SELinux issues.
83
Audit log
The main log file in /var/log/audit/audit.log, which by default contains all messages that are logged by the auditd service. Use 'grep AVC' for SELinux logs.
84
Source context
In SELinux, the context of the processes or users that initiate an action. A context in SELinux is a label that identifies allowed operations. Everything in an SELinux environment has a context.
85
Target context
The SELinux context that is set to a target object, such as a port, file, or directory.
86
Firewall
A solution that can be used to filter packets on a network. Firewalls are used to ensure that only authorized traffic can reach a system. A firewall can be offered through the Linux kernel netfilter functionality but often is also offered as an appliance on the network.
87
Netfilter
The part of the Linux kernel that implements firewalling.
88
iptables
An older solution to create firewall rules on the Linux operating system. It interfaces with the netfilter Linux kernel firewalling functionality and was the default solution to create software firewalls on earlier versions of RHEL. As of RHEL 7, iptables has been replaced by firewalld.
89
nftables
The service that manages kernel firewalling. It is a replacement of the older iptables service. 'nftables' contains the actual firewall while Firewalld is simply a frontend for managing the rules in nftables.
90
Firewalld
The modern service (replacing iptables) that is used since RHEL 7 to implement firewalling based on the Linux kernel firewalling framework.
91
Zone
In firewalld, a collection of one or more network interfaces that specific firewalld rules are associated with.
92
Network Files System (NFS)
A common UNIX solution to export physical file systems to other hosts on the network. The other hosts can mount the exported NFS directory in their local file system.
93
autofs
A service that takes care of automatically mounting file systems at the moment that a specific directory is accessed. This service is very useful to ensure the automatic mounting of home directories for users in a centralized user management system, as can be implemented by the LDAP service.
94
Real-time clock (RTC)
The hardware clock that is installed on the computer motherboard.
95
Hardware time
The time that is provided by computer hardware, typically the BIOS clock. When a Linux system boots, it sets the software time based on the hardware time. Because hardware time often is inaccurate, most Linux systems use the Network Time Protocol (NTP) to synchronize the system time with a reliable time source.
96
Coordinated Universal Time (UTC)
A time standard that is globally the same, no matter which specific time zone a user is in. UTC roughly corresponds to Greenwich Mean Time (GMT).
97
Network Time Protocol
A standard that is used to provide reliable time to servers in a network. NTP on RHEL 9 is implemented by the chronyd service.
98
Stratum
In time synchronization, used to indicate the distance between a server and an authoritative Internet time source.
99
Epoch time
In Linux, the number of seconds that have passed since epoch (corresponds to midnight on January 1, 1970). Some utilities write epoch time instead of real clock time.
100
Container
A ready-to-run application that is started from an image and includes all application dependencies.
101
Container engine
The code that allows containers to run on top of an operating system.
102
Registry
A location where container images are started from.
103
CRI-o
The default container engine on RHEL 9. Pronounced CRY-o.
104
Namespace
An isolated environment that is created by the Linux kernel and allows for running containers in complete isolation. Namespaces exist for multiple aspects of the operating system, including mounts, processes, users, and more.
105
Docker
A common solution to run containers. Docker was the default container solution in RHEL 8 but is no longer supported and was replaced with CRI-o/ podman in RHEL 9.
106
Kubernetes
The standard in container orchestration and also the foundation of Red Hat OpenShift.
107
OpenShift
The Red Hat platform, based on Kubernetes, that is used for container orchestration.
108
Image
The read-only instance from which a container is started.
109
Orchestration
The technique that ensures containers can be offered in a scalable and redundant way in corporate environments.
110
Linger
The Systemd feature that is needed to start Systemd user units at system boot and not at user login.

RHCSA (4 decks)

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