File Details

Question 1

The term file refers to…?

Answer 1

Regular files, directories, symbolic links, device nodes, anothers.

Question 2

All files have common attributes….?

Answer 2

User owner, group owner, permissions, and timing information. This information is stored in a structure called an inode.

Question 3

File names are contained in data structures called…?

Answer 3

dentries (directory entries).

Question 4

A file’s inode information can be examined with the…?

Answer 4

ls -l and stat commands.

Question 5

Within the Linux kernel, files are generally identified by…?

Answer 5

inode number. The ls -i command can be used to examine inode numbers.

Question 6

Three Components Linux associates with a file.

Answer 6

• Data
  The data is the content of the file, in this case, the 16 bytes that compose elvis’s shopping list (13 visible characters, and 3 invisible “return characters that indicate the end of a line). In Linux, as in Unix, every file’s content is stored as a series of bytes.
• Metadata
  In addition to its content, every file in Linux has extra information associated with it. The entire last Workbook focused on some of this information, namely the file’s user owner, group owner, and permissions. Other information, such as the last time the file was modified or read, is stored as well. Much of this metadata is reported when you run the ls -l command. In Linux (and Unix), all of the extra information associated with a file (with the important exception discussed next) is stored in a structure called an inode.

-filename
The filename is the exception to the rule. Although the filename could be considered metadata associated with the file, it is not stored in the inode directly. Instead, the filename is stored in a structure called a dentry. (The term dentry is a shortening of directory entry, and, as we will see in a later Lesson, the structure is closely associated with directories.) In essence, the filename associates a name with an inode.

Question 7

There are ______ structures associated with every file.

Answer 7

Three.

Question 8

Dentry…?

Answer 8

contains a filename and refers to an inode, which contains the file’s metadata and refers to the file’s data.

Question 9

See figure 1.1 for File Structures.

Answer 9

https://academy.redhat.com/courses/rha030-6.1/rha030_fsmngt_filedetail.html#rha030_fsmngt_filedetail_discussion

Question 10

What’s in an inode…?

Answer 10

Stores all the file’s information, except for the filename.

Question 11

What can be found in an inode…?

Answer 11

• Filetype
• Ownerships and Permissions
• Timing Information
• File length and size
• Link Count

Question 12

Inode:

File Type…?

Answer 12

term file has a very general meaning: anything that exists in the filesystem (and thus has an inode associated with it) is a file. This includes regular files and directories, which we have already encountered, symbolic links and device nodes, and a couple more obscure creatures which are related to interprocess communication, and beyond the scope of the course.

Question 13

Possible Linx/Unix File Types:

Regular file’s ls Abbreviation and Use…?

Answer 13

-

Storing data.

Question 14

Possible Linx/Unix File Types:

Directories ls Abbreviation and Use…?

Answer 14

d

Organizing files

Question 15

Possible Linx/Unix File Types:

Symbolic Links ls Abbreviation and Use…?

Answer 15

l

Referring to other files

Question 16

Possible Linx/Unix File Types:

Character Device Nodes ls Abbreviation and Use…?

Answer 16

c

Accessing Devices.

Question 17

Possible Linx/Unix File Types:

Block Device Nodes ls Abbreviation and Use…?

Answer 17

b

Accessing devices

Question 18

Possible Linx/Unix File Types:

Named Pipes ls Abbreviation and Use…?

Answer 18

p

Interprocess communication.

Question 19

Possible Linx/Unix File Types:

Sockets ls Abbreviation and Use…?

Answer 19

s

Interprocess Communication.

Question 20

The seven file types all use the same inode structure, so they each have the same….?

Answer 20

types of attributes: owners, permissions, modify times, etc.

Question 21

Note

Answer 21

The term file is overloaded in Linux (and Unix), and has two meanings. When used in sentences such as “every file has an inode”, the term refers to any of the file types listed in the table above. When used in sentences such as “The head command only works on files, not directories”, the term file is referring only to the specific type of file that holds data. Usually, the meaning is clear from context. When a distinction has to be made, the term regular file is used, as in “The ls -l command identifies regular files with a hyphen (-)”.

Question 22

Ownerships and Permissions….?

Answer 22

very (regular) file and directory has a group owner, a user owner, and a collection of three sets of read, write, and execute permissions. Because this information is stored in a file’s inode, and the inode structure is the same for all files, all seven file types use the same mechanisms for controlling who has access to them, namely chmod, chgrp, and chown.

Question 23

When listing files with ls -l, the first column displays….?

Answer 23

the permissions (as well as file type), the third the user owner, and the fourth the group owner.

Question 24

Timing Information:

Each inode stores three times relevant to the file, conventionally called the…?

Answer 24

atime, ctime, and mtime.

These times record the last time a file was accessed (read), changed, or modified, respectively.

Question 25

File times:

Access Time, Abbreviation and Purpose…?

Answer 25

atime

Updates whenever the file’s data is read.

Question 26

File times:

Change Time, Abbreviation and Purpose…?

Answer 26

ctime

Updates whenever the file’s inode information changes.

Question 27

File times:

Modify Time, Abbreviation and Purpose…?

Answer 27

mtime

Updates whenever the file’s data changes.

Question 28

What’s the difference between change and modify?

Answer 28

When a file’s data changes, the file is said to be modified, and the mtime is updated. When a file’s inode information changes, the file is said to be changed, and the file’s ctime is updated. Modifying a file (and thus changing the mtime) causes the ctime to update as well, while merely reading a file (and thus changing the atime) does not cause the ctime to udpate.

Question 29

What about create time?

Answer 29

Often, people mistake Unix’s ctime for a “creation time”. Oddly, traditional Unix (and Linux) does not record the fixed time a file was created, a fact which many consider a weakness in the design of the Unix filesystem.

Question 30

File length and size…?

Answer 30

The inode records two measures of how large a file is: The file’s length (which is the actual number of bytes of data), and the file’s size (which is the amount of disk space the file consumes). Because of the low level details of how files are stored on a disk, the two differ. Generally, the file’s size increments in chunks (usually 4 kilobytes) at a time, while the length increases byte by byte as information is added to the file. When listing files with the ls -l command, the file’s length (in bytes) is reported in the 5th column. When listing files with the ls -s command, the file’s size (in kilobytes) is reported instead.`

Question 31

Link Count…?

Answer 31

Lastly, the inode records a file’s link count, or the number of dentries (filenames) that refer to the file. Usually, regular files only have one name, and the link count as one. As we will find out, however, this is not always the case. When listing files with ls -l, the second column gives the link count.

Question 32

Red Hat Enterprise Linux includes the stat command for examining a file’s inode information in detail. In Unix programming, a file’s collection of inode information is referred to as the status of the file. The stat command can be thought of as reporting the…?

Answer 32

status of a file.

Question 33

Stat switch:

-c, –format=FORMAT…?

Answer 33

Print only the requested information using the specified format. See the stat(1) man page for more information.

Question 34

Stat switch:

-f, –filesystem…?

Answer 34

Show information about the filesystem the file belongs to, instead of the file.

Question 35

Stat switch:

-t, –terse…?

Answer 35

Print output in terse (single line) form.

Question 36

While the stat command is convenient for listing the inode information of individual files, the ls command often does a better job…?

Answer 36

summarizing the information for several files.

Question 37

ls switch:

-a, –all…?

Answer 37

Include files that start with .

Question 38

ls switch:

-d, –directory…?

Answer 38

If FILE is a directory, list information about the directory itself, not the directory’s contents.

Question 39

ls switch:

-F, –classify

Answer 39

Decorate filenames with one of *,/,-,@, or | to indicate file type.

Question 40

ls switch:

-h, –human-readable…?

Answer 40

Use “human readable” abbreviations when reporting file lengths.

Question 41

ls switch:

-i, –inode…?

Answer 41

List index number of each file’s inode.

Question 42

ls switch:

-l…?

Answer 42

Use long listing format.

Question 43

ls switch:

-n, –numeric-uid-gid

Answer 43

Use numeric UIDs and GIDs, rather then usernames and groupnames.

Question 44

ls switch:

-r, –reverse…?

Answer 44

Reverse sorting order.

Question 45

ls switch:

-R –recursive…?

Answer 45

List subdirectories recursively.

Question 46

ls switch:

–time=WORD…?

Answer 46

Report (or sort by) time specified by WORD instead of mtime. WORD may be one of “atime”, “access”, “ctime”, or “status”.

Question 47

ls switch:

-t…?

Answer 47

Sort by modification time.

Question 48

While people tend to use filenames to identify files, the Linux kernel usually uses…?

Answer 48

the inode directly. Within the filesystem, every inode is assigned a unique inode number. The inode number of a file can be listed with the -i command line switch to the ls command.

Question 49

when using ls -s command, next to each filename, the ls command reports…?

Answer 49

the size of the file in kilobytes. (For example ash takes up 96 Kbytes of disk space. In the (abbreviated) output, that all of the sizes are divisible by four. Apparently, when storing a file on the disk, disk space gets allocated to files in chunks of 4 Kbytes. (This is referred to as the “blocksize” of the filesystem).