Chapter 5

Question 1

ACL

Answer 1

An access control list (ACL) is a list of users or groups and the permissions they’re given. Linux ACLs, like Linux owner, group, and world permissions, consist of three permission bits, one each for read, write, and execute permissions. The file’s owner can assign ACLs to an arbitrary number of users and groups, making ACLs more flexible than Linux permissions, which are limited to groups defined by the system administrator.

Question 2

cp

Answer 2

The cp command copies a file.

Question 3

cpio

Answer 3

cpio
The cpio program is similar in principle to tar, but the details of its operation differ. As with tar, you can direct its output straight to a tape device or to a regular file. Backing up to a tape device can be a convenient way to back up the computer because it requires no intermediate storage. To restore data, you use cpio to read directly from the tape device file or from a regular file.

Question 4

Disk quota

Answer 4

A limit on the amount of disk space that an individual or group may use.

Question 5

FAT

Answer 5

FAT
A simple filesystem using a table to index files on a block device (floppy or hard disk). It comes in the varieties of FAT-12 (MS-DOS), FAT-16 (MS-DOS, MS-Windows 3.x) and “FAT-32” (MS-Windows 9x).

Question 6

FHS

Answer 6

A standard that defines the names and contents of critical directories in a Linux filesystem (meaning 2).

Question 7

File globbing

Answer 7

The process of wildcard expansion-for instance, matching the existing file glossary.txt when the string glos*.txt is typed. Also called globbing.

Question 8

Filesystem Hierarchy Standard (FHS)

Answer 8

A standard that defines the names and contents of critical directories in a Linux filesystem (meaning 2).

Question 9

Filesystem Standard (FSSTND)

Answer 9

An early attempt to define the names and contents of critical directories in a Linux filesystem (meaning 2). The FSSTND has been supplanted by the FHS.

Question 10

FSSTND

Answer 10

An early attempt to define the names and contents of critical directories in a Linux filesystem (meaning 2). The FSSTND has been supplanted by the FHS.

Question 11

GID

Answer 11

A number associated with a particular group. Similar to a user ID (UID).

Question 12

Globbing

Answer 12

Filename expansion using asterisks (*), question marks (?), and so on is sometimes called globbing.

Question 13

Group ID (GID)

Answer 13

A number associated with a particular group. Similar to a user ID (UID).

Question 14

Hard Link

Answer 14

A directory entry for a file that has another directory entry. All hard links are equally valid ways of accessing a file, and all must be deleted in order to delete a file. See also soft link.

Question 15

Incremental backup

Answer 15

Incremental backup
A type of backup in which only files that have changed since the last backup are backed up. This is used to reduce the time required to back up a computer, at the cost of potentially greater restoration complexity.

Question 16

Is

Answer 16

The ls command displays the names of files in a directory.

Question 17

mkdir

Answer 17

The mkdir command creates a directory.

Question 18

mv

Answer 18

The mv command (short for move) is commonly used both to move files and directories from one location to another and to rename them. Linux doesn’t distinguish between these two types of operations, although many users do.

Question 19

Permission Bit

Answer 19

A single bit used to define whether a given user or class of users has a particular type of access to a file. For instance, the owner’s execute permission bit determines whether the owner can run a file as a program. The permission bits together make up the file’s mode.

Question 20

rm

Answer 20

To delete a file, use the rm command, whose name is short for remove.

Question 21

rmdir

Answer 21

The rmdir command is the opposite of mkdir; it destroys a directory.

Question 22

SGID

Answer 22

The set group ID (SGID) option is similar to the SUID option, but it sets the group of the running program to the group of the file. It’s indicated by an s in the group execute bit position in the permission string, as in rwxr-sr-x. When the SGID bit is set on a directory, new files or subdirectories created in the original directory will inherit the group ownership of the directory, rather than be based on the user’s current default group.

Question 23

Shareable files

Answer 23

Files that can be reasonably shared with another computer, as in users’ home directory files and program files in /opt or /usr.

Question 24

Socket

Answer 24

A programming construct enabling connection to network connection endpoints (the combination of IP addresses and port numbers).

Question 25

Soft link

Answer 25

A type of file that refers to another file on the computer. When a program tries to access a soft link, Linux passes the contents of the linked-to file to the program. If the linked-to program is deleted, the soft link stops working. Deleting the soft link doesn’t affect the original file. Also referred to as a symbolic link. See also hard link.

Question 26

Sticky Bit

Answer 26

The sticky bit has changed meaning during the course of Unix history. In modern Linux implementations (and most modern versions of Unix), it’s used to protect files from being deleted by those who don’t own the files. When this bit is present on a directory, the directory’s files can be deleted only by their owners, the directory’s owner, or root. The sticky bit i indicated by a t in the world execute bit position, as in rwxr-xr-t.

Question 27

SUID

Answer 27

The set user ID (SUID) option is used in conjunction with executable files, and it tells Linux to run the program with the permissions of whoever owns the file rather than with the permissions of the user who runs the program.

Question 28

Superuser

Answer 28

A user with extraordinary rights to manipulate critical files on the computer. The superuser’s username is normally root.

Question 29

Symbolic link

Answer 29

A type of file that refers to another file on the computer. When a program tries to access a soft link, Linux passes the contents of the linked-to file to the program. If the linked-to program is deleted, the soft link stops working. Deleting the soft link doesn’t affect the original file. Also referred to as a symbolic link. See also hard link.

Question 30

tar

Answer 30

The tar program’s name stands for “tape archiver.” Despite this fact, you can use tar to archive data to other media. In fact, tarballs (archive files created by tar and typically compressed with gzip or bzip2) are often used for transferring multiple files between computers in one step, such as when distributing source code.

Question 31

UID

Answer 31

A number associated with a particular account. Linux uses the UID internally for most operations, and it converts to the associated username only when interacting with people.

Question 32

umask

Answer 32

A bit pattern representing the permission bits that are to be removed from new files as they’re created by processes.

Question 33

User ID (UID)

Answer 33

A number associated with a particular account. Linux uses the UID internally for most operations, and it converts to the associated username only when interacting with people.

Question 34

Variable

Answer 34

In computer programming or scripting, a placeholder for data. Variables may change from one run of a program to another or even during a single run of a program.

Question 35

Variable file

Answer 35

A file whose data may change at any time. Examples include user data files and queues maintained by servers.

Question 36

whereis

Answer 36

The whereis program searches for files in a restricted set of locations, such as standard binary file directories, library directories, and man page directories. This tool does not search user directories or many other locations that are easily searched by find or locate.

Question 37

Wildcard

Answer 37

A character or group of characters that, when used in a shell as part of a filename, matches more than one character. For instance, b??k matches book, back, and buck, among many other possibilities.