Linux+ Chapter4

Front 1

filenames can begin with a dot and ....

Back 1

These socalled dot files are hidden from view by most utilities that display files, so they’re popular for storing configuration files in your home directory.

Front 2

single dot (.) refers to

filename that consists of a double dot (..) refers to

Back 2

(.) current dir

(..) refers to the parent directory

Front 3

Characters enclosed in square brackets ([]) normally match

Back 3

any character in the set.
For instance, b[ao][lo]k matches balk and book but not buck
For instance, b[a-z]ck matches back, buck, and other four-letter filenames of this form whose second character is a lowercase letter

Front 4

ls Command

Back 4

ls [options] [files]

ls command displays the names of files in a directory

Front 5

ls options
-a
--color
-d
-l

Back 5

-a or --all parameter displays dot files
--color option produces a color-coded listing that differentiates directories, symbolic links, and so on by displaying them in different colors
-d or --directory parameter changes this behavior to list only the directory name, which is sometimes preferable
-l produces a long listing that includes information such as the file’s permission strin

Front 6

ls options
-F

Back 6

-F or --file-type option appends an indicator code to the end of each name so you know what type of file it is. the meanings are as follows:
/ Directory
@ Symbolic link
= Socket
| Pipe

Front 7

ls options
-R

Back 7

-R or --recursive option causes ls to display directory contents recursively. That is, if the target directory contains a subdirectory, ls displays both the files in the target directory and the files in its subdirectory

Front 8

cp Command

Back 8

copies a file

cp [options] source destination

Front 9

cp options
-f
-i
-p

Back 9

-f or --force option forces the system to overwrite any existing files without prompting

-i or --interactive option causes cp to ask you before overwriting any existing files.

-p or --preserve option preserves ownership and permissions, if possible.

Front 10

cp options
-R
-a
-u

Back 10

-R or --recursive option and specify a directory as the source, the entire directory, including its subdirectories, is copied.

-a or --archive option is similar to -R, but it also preserves ownership and copies links as is

-u or --update option tells cp to copy the file only if the original is newer than the target or if the target doesn’t exist

Front 11

ollowing command copies the /etc/fstab configuration file to a backup location in /root, but only if the original /etc/fstab is newer than the existing backup

Back 11

# cp -u /etc/fstab /root/fstab-backup

Front 12

mv Command

Back 12

mv command (short for move) is commonly used both to move files and directories from one location to another and to rename them

mv [options] source destination

Front 13

mv options
-f
-i

Back 13

-f or --force option forces the system to overwrite any existing files without prompting

-i or --interactive option causes cp to ask you before overwriting any existing files.

Front 14

command copies the document.odt file into the important/purchases subdirectory

Back 14

$ mv document.odt important/purchases/

Front 15

touch Command

Back 15

Linux-native filesystems maintain three time stamps for every file:
- Creation time
- Last modification time
- Last access time

touch [options] files

1)By default, touch sets the modification and access times to the current time
2)the specified files don’t already exist, touch creates them as empty files

Front 16

touch options
-a
-m
-c
-t

Back 16

-a or --time=atime option causes touch to change the access time alone
-m or --time=mtime option causes touch to change the modification time alone
-c or --no-create option If you don’t want touch to create any files that don’t already exist
-t timestamp option sets the time to the specified timestam

Front 17

tar Utility

Back 17

tar program’s name stands for “tape archiver”

Front 18

tar cmds
--create

--concatenate

--append

--update

Back 18

abr
--create - c - Creates an archive
--concatenate - A - Appends tar files to an archive
--append - r - Appends non-tar files to an archive
--update - u - Appends files that are newer than those in an archive

Front 19

tar cmds
--diff or --compare

--list

--extract or --get

Back 19

abr
--diff or --compare - d - Compares an archive to files on disk
--list - t - Lists an archive’s contents
--extract or --get - x - Extracts files from an archive

Front 20

tar qualifiers
--directory dir

--file [host:]file

--listed-incremetnal file

Back 20

abr
--directory dir - C - Changes to directory dir before performing operations
--file [host:]file - f - Uses the file called file on the computer called host as the archive file
--listed-incremental file - g - Performs an incremental backup or restore, using file as a list of previously archived files

Front 21

tar qualifiers
--one-file-system
--multi-volume
--tape-lenth N
--same-permissions

Back 21

--one-file-system - l - Backs up or restores only one filesystem (partition)
--multi-volume - M - Creates or extracts a multi-tape archive
--tape-length N - L - Changes tapes after N kilobytes
--same-permissions - p - Preserves all protection information

Front 22

tar qualifiers
--absolute-paths
--verbose
--verify
--exclude file

Back 22

--absolute-paths - P - Retains the leading / on filenames
--verbose - v - Lists all files read or extracted; when used
with --list, displays file sizes, ownership, and time stamps
--verify - W - Verifies the archive after writing it
--exclude file - (none) - Excludes file from the archive

Front 23

tar qualifiers
--exclude-from file
--gzip or --ungzip
--bzip2

Back 23

--exclude-from file - X - Excludes files listed in file from the archive
--gzip or --ungzip - z - Processes an archive through gzip
--bzip2 - j - Processes an archive through bzip2

Front 24

archiving and compressing the my-work subdirectory of your home directory to a USB pen drive mounted at /media/pen

Back 24

$ tar cvfz /media/pen/my-work.tgz ~/my-work

Front 25

pen drive to another system, mount it at /media/usb, and want
to extract the archive, you can do so with another command

Back 25

$ tar xvfz /media/usb/my-work.tgz

Front 26

cpio Utility

Back 26

cpio program is similar in principle to tar, but the details of its operation differ.

Front 27

The cpio utility has three operating modes:

Back 27

Copy-out mode
This mode, activated by use of the -o or --create option, creates an archive and copies files into it.
Copy-in mode
You activate copy-in mode by using the -i or --extract option. This mode extracts data from an existing archive. If you provide a filename or a pattern to match, cpio extracts only the files whose names match the pattern you provide.
Copy-pass mode
This mode is activated by the -p or --pass-through option. It combines the copy-out and copy-in modes, enabling you to copy a directory tree from one location to another.

Front 28

Options for Use with cpio
--reset-access-time
--append
--pattern-file=filename
--file=filename

Back 28

--reset-access-time - abbr - -a Resets the access time after reading a file so that it doesn’t appear to have been read.
--append - abbr -A - Appends data to an existing archive.
--pattern-file=filename - abbr. -E filename - Uses the contents of filename as a list of files to be extracted in copy-in mode.
--file=filename - abbr -F filename - Uses filename as the cpio archive file; if this parameter is omitted, cpio uses standard input or output.

Front 29

Options for Use with cpio
--format=format
-I filename
--no-absolute-filenames
-O filename

Back 29

--format=format -H format Uses a specified format for the archive file. Common values for format include bin (the default, an old binary format), crc (a newer binary format with a checksum), and tar (the format used by tar).
-I filename Uses the specified filename instead of standard input.
--no-absolute-filename - In copy-in mode, extracts files relative to the current directory, even if filenames in the archive contain full directory paths.
-O filename Uses the specified filename instead of standard output

Front 30

Options for Use with cpio
--list
--unconditional
--verbose

Back 30

--list - abbr -t - Displays a table of contents for the input.

--unconditional - abbr -u - Replaces all files without first asking for
verification.

--verbose - abbr -v - Displays filenames as they’re added to or
extracted from the archive. When used with -t, displays additional listing information (similar to ls -l).

Front 31

use cpio to archive a directory, you must pass a list of files to the utility using standard input

Back 31

$ find ./my-work | cpio -o > /media/pen/my-work.cpio

Front 32

use cpio to archive a directory, you must pass a list of files to the utility using standard input with compression

Back 32

$ find ./my-work | cpio -o | gzip > /media/pen/my-work.cpio.gz

Front 33

Extracting data from an uncompressed cpio archive (say, on another computer with the media mounted at /media/usb) entails using the -i option, but no pipe is required:

Back 33

$ cpio -i < /media/usb/my-work.cpio

Front 34

If your cpio archive is compressed, you must first uncompress it with gunzip. By using the -c option to this command, you can pass its output to cpio in a pipe:

Back 34

$ gunzip -c /media/usb/my-work.cpio.gz | cpio -i

Front 35

dd Utility

Back 35

archive a filesystem at a very low level. This utility is a low-level copying program, and when it’s given the device file for a partition as input, it copies that partition’s contents to the output file you specify.

# dd if=/dev/sda3 of=/dev/st0

Front 36

backs up the /dev/sda3 disk partition to /dev/st0 (a SCSI tape drive).

Back 36

# dd if=/dev/sda3 of=/dev/st0

Front 37

dd restore from /dev/sda3

Back 37

# dd if=/dev/st0 of=/dev/sda3

Front 38

dd utility shortcoming

Back 38

good way to create exact backups of entire partitions but
backs up the entire partition, including any empty space
Restoring individual files is also impossible unless the target device is a random access device that can be mounted
you can’t easily restore data to a partition that’s smaller than the original partition

good for CD-ROM

Front 39

/dev/zero device

Back 39

a Linux device that returns nothing but zeroes

Front 40

if you need an empty file of a
particular size

Back 40

$ dd if=/dev/zero of=empty-file.img bs=1024 count=720

creates a 720KB (1024 × 720 bytes) empty file

Front 41

In Linux, a link is a ?

Back 41

In Linux, a link is a way to give a file multiple identities, similar to shortcuts in Windows and aliases in Mac OS.

Front 42

Two types of links exist:

Back 42

hard links and soft links (a.k.a.
symbolic links).

Front 43

ln command

Back 43

ln command creates links.

ln [options] source link

source is the original file, and the link is the name of the link you want to create

Front 44

ln cmd options
-f
-i
-d, -F
-s

Back 44

-f or --force option
causes ln to remove any existing links or files that have the target link name
-i or --interactive option
causes ln to remove any existing links or files that have the target link name but queireis
-d, -F, or --directory
Ordinarily, you can’t create hard links to directories. The root user can attempt to do so, though, by passing the -d, -F, or --directory option to ln
-s or --symbolic option
ln command creates hard links by default. To create a symbolic
link, use -s

Front 45

mkdir Command

Back 45

mkdir command creates a directory

mkdir [options] directory-name(s)

Front 46

mkdir options
-m
-p

Back 46

-m mode or --mode=mode option causes the new directory to have the specified permission mode, expressed as an octal number
-p or --parents option
if you specify the creation of a directory within a directory that doesn’t exist, mkdir responds with a No such file or directory error with -p option creates the parent

Front 47

rmdir Command

Back 47

destroys a directory

rmdir [options] directory-name(s)

Front 48

delete one/two/three, then
one/two, and finally one

Back 48

rmdir -p one/two/three

-p or --parents option causes rmdir to delete an entire directory tree

Front 49

learn who owns a file

Back 49

ls command

$ ls -l
total 1141
-rw-r--r-- 1 rodsmith users 219648 Mar 8 13:06 4425ch02.doc
-rw-r--r-- 1 rodsmith users 942590 Mar 6 23:31 f0201.tif

rodsmith - username of the owner
users - group name

Front 50

Changing a File’s Owner

Back 50

change a file’s ownership using the chown command

chown [options] [newowner][:newgroup] filenames

Front 51

chown option
-R

Back 51

-R or --recursive, which implements the ownership change on an entire directory tree.

Front 52

Changing a File’s Group

Back 52

changes a file’s group

chgrp [options] newgroup filenames

Front 53

file type code

Back 53

ls -l test
-rwxr-xr-x 1 rodsmith users 111 Apr 13 13:48 test

The first character has special meaning—it’s the file type code. The type code determines how Linux will interpret the file—as ordinary data, a directory, or a special file type

Front 54

Linux File Type Codes
-
d
l
p

Back 54

- Normal data file;

d Directory;

l Symbolic link; the file contains the name of another file or directory. When Linux accesses the symbolic link, it tries to read the linked-to file.

p Named pipe; a pipe enables two running Linux programs to communicate with each other.

Front 55

Linux File Type Codes
s
b
c

Back 55

s Socket; a socket is similar to a named pipe, but it permits network and bidirectional links.

b Block device; a file that corresponds to a hardware device to and from which data is transferred in blocks of more than one byte. Disk devices (hard disks, floppies, CD-ROMs, and so on) are common block devices

c Character device; a file that corresponds to a hardware device to and from which data is transferred in units of one byte. Examples include parallel and RS-232 serial port devices.

Front 56

Meanings of Permission Bits
2 to 10

Back 56

$ ls -l test
-rwxr-xr-x 1 rodsmith users 111 Apr 13 13:48 test
first char - file type code
2 to 10 are broken in 3 groups of 3 chars:
first group controls the file owner's access to files
second group controls the group's access to the file
third controls all other users' access to the file

Front 57

Meanings of Permission Bits (2 to 10) each group (permission string)

Back 57

the permission string determines the presence or absence of each of three types of access: read, write, and execute.
The absence of the permission is denoted by a dash (-) in the permission string.

Front 58

permission bits (def)

Back 58

Individual permissions, such as execute access for the file’s owner, are often referred to as permission bits
one digit for each of the owner, group, and world permissions
1 for execute permission,
2 for write permission, and
4 for read permission

Front 59

permission string vs octal code
rwxrwxrwx

rwxr-xr-x

rwxr-x---

Back 59

rwxrwxrwx - 777 - Read, write, and execute permissions for all users.
rwxr-xr-x - 755 - Read and execute permission for all users. The file’s owner also has write permission.
rwxr-x--- - 750 - Read and execute permission for the owner and group. The file’s owner also has write permission. Users who
aren’t the file’s owner or members of the group have no access to the file.

Front 60

permission string vs octal code
rwx------
rw-rw-rw-
rw-rw-r--

Back 60

rwx------ - 700 - Read, write, and execute permissions for the file’s owner only; all others have no access.
rw-rw-rw- - 666 - Read and write permissions for all users. No execute permissions for anybody.
rw-rw-r-- - 664 - Read and write permissions for the owner and group. Read-only permission for all others.

Front 61

permission string vs octal code
rw-rw----
rw-r--r--
rw-r-----

Back 61

rw-rw---- - 660 - Read and write permissions for the owner and group. No world permissions.
rw-r--r-- - 644 - Read and write permissions for the owner. Read-only permission for all others.
rw-r----- - 640 - Read and write permissions for the owner, and readonly permission for the group. No permission for others.

Front 62

permission string vs octal code
rw-------
r--------

Back 62

rw------- - 600 - Read and write permissions for the owner. No permission for anybody else.
r-------- - 400 - Read permission for the owner. No permission for anybody else.

Front 63

Symbolic links are unusual with respect to permissions

Back 63

This file type always has 777 (rwxrwxrwx) permissions, thus granting all users full access to the file. This access applies
only to the link file itself, however, not to the linked-to file

Front 64

SUID

Back 64

Set user ID (SUID)
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
SUID programs are indicated by an s in the owner’s execute bit position in the permission string, as in
rwsr-xr-x.

Front 65

SGID

Back 65

set group ID (SGID)
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

Front 66

Sticky bit

Back 66

In modern Linux implementations
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 is indicated by a t in the world execute bit position, as in rwxr-xr-t.

Front 67

Linux ACLs

Back 67

new and improved permission system
consist of three permission bits, one each for read, write, and execute permissions
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

ACLs require their own commands to set and view. The setfacl command sets an ACL, and the getfacl command displays the ACLs for a file.

Front 68

command sets an ACL
command displays the ACLs for a file

Back 68

setfacl
getfacl

Front 69

suppose you’ve acquired a script called bigprogram. You want to set both SUID and SGID bits (6); to make the program readable, writeable, and executable by the owner (7); to make it readable and executable by the group (5); and to make it completely inaccessible to all others (0).

Back 69

$ ls -l bigprogram
-rw-r--r-- 1 rodsmith users 10323 Oct 31 18:58 bigprogram
$ chmod 6750 bigprogram
$ ls -l bigprogram
-rwsr-s--- 1 rodsmith users 10323 Oct 31 18:58 bigprogram

Front 70

symbolic mode permission set code

Back 70

u - Owner
g - Group
o - World
a - All

Front 71

symbolic mode change type code

Back 71

+ - Add
- - Remove
= - set equal to

Front 72

symbolic mode permissions to modify code

Back 72

r - Read
w - Write
x - Execute
X - Execute only if the file is a dir or already has execute permission
s - SUID or SGID
t - Sticky bit
u - existing owner's permissions
g - existing group permission
0 - existing world permissions

Front 73

rw-r--r--
chmod a+x bigprogram will cause

Back 73

rw-r--r--
chmod a+x bigprogram will cause
rwxr-xr-x

Front 74

r--------
chmod ug=rw report.tex

Back 74

r--------
chmod ug=rw report.tex
rw-rw----

Front 75

rwxrwxr-x
chmod o-rwx bigprogram

Back 75

rwxrwxr-x
chmod o-rwx bigprogram
rwxrwx---

Front 76

rw-r--r--
chmod g=u report.tex

Back 76

rw-r--r--
chmod g=u report.tex
rw-rw-r--

Front 77

rw-rw-rw-
chmod g-w,o-rw report.tex

Back 77

rw-rw-rw-
chmod g-w,o-rw report.tex
rw-r-----

Front 78

umask command

Back 78

When a user creates a file, that file has default ownership and permissions.
The default group is the user’s primary group.
The default permissions are configurable. These are defined by the user mask (umask), which is set by the umask command

Front 79

Special Permission Bits list

Back 79

SUID - Set user ID
SGID - Set group ID
Sticky bit

Front 80

When a user creates a file what ownership and permissions are

Back 80

When a user creates a file, that file has default ownership and permissions. The default owner is, user who created the file.
The default group is the user's primary group.
Permissions are configurable with user mask which is manipulated by umask command

Front 81

Sample Umask Values and Their Effects
000
002
022

Back 81

Umask - Created Files - Created Dir
000 - 666 (rw-rw-rw-)- 777 (rwxrwxrwx)
002 - 664 (rw-rw-r--) - 775 (rwxrwxr-x)
022 - 644 (rw-r--r--) - 755 (rwxr-xr-x)

Front 82

Sample Umask Values and Their Effects
027
077
277

Back 82

Umask - Created Files - Created Dir
027 - 640 (rw-r-----) - 750 (rwxr-x---)
077 - 600 (rw-------) - 700 (rwx------)
277 - 400 (r--------) - 500 (r-x------)

Front 83

How superuser can set default setting fro all users

Back 83

Edit
/etc/profile
contains unmask commands

Front 84

find what the current umask is use

Back 84

umask -S

Front 85

umask u=rwx,g=rx,o=rx is equivalent to

Back 85

umask 022

Front 86

users can change their default group
with

Back 86

newgrp

newgrp skyhook
create new files with the group set to the skyhook group

Front 87

newgrp -l <group> cmd

Back 87

newgrp -l skyhook, which reinitializes the
environment as if the user had just logged in.

Front 88

chattr command

Back 88

allows you to change file attributes

Front 89

chattr command options
a
c
i
j

Back 89

a - append only
sets append mode, which disables writes access but allows append
c - compressed
causes the kernel to automatically compress data written to the file and uncompress it when it's read back
i - immutable
makes file immutable, can't be deleted, links to it can't be created, and file can't be renameed
j - data journaling
tells the kernel to journal all data wrtten to the file

Front 90

chattr command options
s
t
A

Back 90

s - secure deletion
when you delete a file it might still be available for recycling with s kernel zeros its data blocks
t - no tail-merging
A - no access time updates
Linux won't update the access time stamp when you access a file

Front 91

Tail-merging def

Back 91

is a process in which small pieces of data at the ends of files that don’t fill a complete block are merged with similar pieces of data from other files. The result is reduced disk space consumption

Front 92

cmd to add the immutable flag to the important.txt

Back 92

# chattr +i important.txt

to remove the immutable

# chattr -i important.txt

Front 93

Two general quota support systems are available for Linux

Back 93

quota v1 support - up to 2.4.x kernel
quota v2 system - added after 2.6.x

Front 94

How is the package called that is used for the quota v2 system

Back 94

called quota

it installs a number of utilities, configuration files, SysV startup scripts

Front 95

what you must modify for any partitions on which you want to use quota support

Back 95

You must modify your /etc/fstab entries for any partitions on which you want to use
quota support.

/dev/hdc5 /home ext3 usrquota,grpquota 1 1

This line activates both user and group quota support for the /dev/hdc5 partition which is mounter at /home

Front 96

How can you set the quotas

Back 96

edquota

which starts the Vi editor on a temporary configuration file (/etc/quotatab) that controls quotas for the user you specify.
When you exit the utility, edquota uses the temporary configuration file to write the quota information to low-level disk data structures that control the kernel’s quota mechanisms.

Front 97

edquota -t

Back 97

set the grace period by using edquota with its -t option
Grace periods are set on a per-filesystem basis rather than a per-user basis

Front 98

quotacheck

Back 98

which verifies and updates quota information on quota-enabled disks

Front 99

repquota

Back 99

repquota, which summarizes the quota information about the filesystem you specify or on all filesystems if you pass it the -a option.

Front 100

quota -g
quota -l
quota -q

Back 100

quota -g
displays group quotas

quota -l
omits NFS mounts

quota -q
limits output to filesystems on which usage is over the limit

Front 101

FSSTND (abbr and def)

Back 101

FSSTND - Filesystem Standard

FSSTND standardized several specific features
1)Standardized t NN he programs that reside in /bin and /usr/bin. Differences on this score
caused problems when scripts referred to files in one location or the other
2)Specified that executable files NN shouldn’t reside in /etc, as had previously been common.
3)Removed changeable files from the /usr directory tree, enabling it to be mounted readonly (a useful security measure)

Front 102

FHS

Back 102

FHS - Filesystem Hierarchy Standard
is based on FSSTND but extends it substantially

Front 103

FHS shareable file

Back 103

Shareable files may be reasonably shared between computers, such as user data files and program binary files. If files are shared, they’re normally shared through an NFS server

Front 104

FHS unshareable file

Back 104

contain system-specific information, such as configuration files. For instance, you’re not likely to want to share a server’s configuration file between computers

Front 105

FHS static files

Back 105

don’t normally change except through direct intervention by the
system administrator

Front 106

FHS variable files

Back 106

Variable files may be changed by users, automated scripts, servers, or the like

Front 107

FHS /

Back 107

every Linux filesystem traces its roots to the root filesystem/dir

Front 108

Where /etc and /sbin should be location

Back 108

must reside on the root partition

Front 109

FHS /boot

Back 109

/boot directory contains static and unshareable files related to the initial booting
of the computer.

Front 110

FHS /etc

Back 110

Higher-level startup and configuration files reside in /etc

Front 111

FHS /bin

Back 111

This directory contains certain critical executable files, such as ls, cp, and mount. These commands are accessible to all users and constitute the most important commands
that ordinary users might issue

Front 112

FHS /sbin

Back 112

directory is similar to /bin, but it contains programs that are normally run only by the system administrator—tools like fdisk and e2fsck

Front 113

FHS /lib

Back 113

similar to /bin and /sbin
it contains program libraries, which are made up of code that’s shared across many programs and stored in separate files to save disk space and RAM

Front 114

/lib/modules

Back 114

/lib/modules subdirectory contains kernel modules—drivers that can be loaded and unloaded as required.

Front 115

FHS /usr

Back 115

hosts the bulk of a Linux computer’s programs

Front 116

FHS /usr/local

Back 116

contains subdirectories that mirror the organization of /usr, such as /usr/local/bin and /usr/local/lib.
/usr/local directory hosts files that a system administrator installs locally

Front 117

FHS /usr/X11R6

Back 117

houses files related to the X Window System

Front 118

FHS /opt

Back 118

similar to /usr/local in many ways, but it’s intended for readymade packages that don’t ship with the OS, like commercial word processors or games. Typically, these programs reside in subdirectories in /opt named after themselves, such as /opt/applix.

Front 119

FHS /home

Back 119

This directory contains users’ data, and it’s shareable and variable. Although the /home
directory is considered optional in FHS, in practice it’s a matter of the name being optional.

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FHS /root

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home directory for the root user. Because the root account is so critical and system specific, this variable directory isn’t really shareable.

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FHS /var

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contains transient files of various types--system log files, print spool files, mail and news files, and so on

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FHS /tmp

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Many programs need to create temporary (hence variable) files, and the usual place
to do so is in /tmp.

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FHS /mnt

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Linux mounts removable-media devices within its normal directory structure, and
/mnt is provided for this purpose

/mnt, such as /mnt/floppy and /mnt/cdrom, to function as mount points

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FHS /media

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This directory is an optional part of the FHS. It’s like /mnt, but it should contain
subdirectories for specific media types, such as /media/floppy and /media/cdrom. Many modern distributions use /media subdirectories as the default mount points for common removable disk types.

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FHS /dev

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Linux treats most hardware devices as if they were files, the OS must have a location in its filesystem where these device files reside. The /dev directory is that place. It contains a large number of files that function as hardware interfaces.

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FHS /proc

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This is an unusual directory because it doesn’t correspond to a regular directory or partition. Instead, it’s a virtual filesystem that’s created dynamically by Linux to provide access to certain types of hardware information that aren’t accessible via /dev

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displaying information about your
CPU—its model name, speed, and so on

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cat /proc/cpuinfo

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find Command

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find utility implements a brute-force approach to finding files

find [path...] [expression...]

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find
-name pattern

-perm mode

-gid GID

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-name pattern
You can search for a filename using the -name pattern expression doing so finds files that match the specified pattern

-perm mode
If you need to find files that have certain permissions, you can do so by using the -term mode expression

-gid GID
searches for files whose group ID (GID) is set to GID

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find
-size n

-group name

-uid UID

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-size n
You can search for a file of a given size

-group name
option locates files whose group name is name

-uid UID
searches for files owned by the user whose
user ID (UID) is UID

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find
-user name

-maxdepth levels

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-user name
searches for files owned by name

-maxdepth levels
If you want to search a directory and, perhaps, some limited number of subdirectories, you can use the -maxdepth levels expression to limit the search

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consider the task of finding all C source code files, which normally have names that end in .c, in all users’ home directories. If these home directories reside in /home, you might issue the following command:

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# find /home -name “*.c”

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locate cmd

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locate utility works much like find if you want to find a file by name, but it differs in two important ways

1)far less sophisticated in its search options. You normally use it to search only on filenames, and the program returns all files that contain the specified string. For instance, when searching for rpm, locate will return other programs, like gnorpm and rpm2cpio.
2)locate program works from a DB that it maintains Most distributions include a cron job that calls locate with options that cause it to update its database periodically, such as once a night or once a week

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slocate cmd

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Some Linux distributions use slocate rather than locate

slocate program includes security features to prevent users from seeing the names of files in directories they shouldn’t be able to access

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whereis cmd

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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.

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cmd locates ls

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$ whereis ls
ls: /bin/ls /usr/share/man/man1/ls.1.bz2

result shows both the ls executable (/bin/ls) and the ls man page

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which cmd

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Considered as a search command, which is very weak; it merely searches your path for the command that you type and lists the complete path to the first match it find.
For instance, you might want to know
where the xterm program is located:

$ which xterm
/usr/bin/xterm

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type Command

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ommand isn’t really a search command; instead, it tells you how a command you
type will be interpreted—as a built-in command, an external command, an alias, and so on.

$ type type
type is a shell builtin
$ type cat
cat is /bin/cat
$ type ls
ls is aliased to `ls --color’