LQWiki - User contributions [en]

Su

2021-07-27T01:29:00Z

4dummies: Alphabetize related commands; add runuser(1) to the llist

The '''su''' [[command]] allows the current user to assume the identity of another user on a [[Linux]] system. It stands for "switch user" or "substitute user", ''not'' "superuser" (although it defaults to prompting for the [[root]] password if invoked without any arguments). The <tt>su</tt> command is very useful in [[Unix]].

== Usage ==
<pre>
$ su [user]
</pre>

When an ordinary user invokes the <tt>su</tt> command they will be prompted for the password of the user whose account they are attempting to utilise. Once a correct password is entered, the [[shell]] prompt will return and the user will now be operating with the [[permission]]s and access privileges of the target account. If the command <tt>su -</tt> is used (with a single dash as the argument) the user will also inherit the environment of the target user (as if they had logged in using the target user's ID and password).

It is often suggested that as a precaution when using <tt>su</tt> to execute commands as the root user, that the command be invoked in the form:

<pre>
$ su -c command [user]
</pre>

When executed in this form, if authentication is successful, <tt>su</tt> will return immediately after executing <tt>command</tt> as the other user, without launching a shell as the target user. If the target user is root, this method of execution will avoid problems caused by accidentally leaving a root shell open on the system.

In most shells <tt>command</tt> must be contained within quotation marks if it contains special characters or spaces.

As an example, an unprivileged user might execute the following command to edit the [[LILO]] configuration file:

<pre>
$ su -c "vi /etc/lilo.conf"
</pre>

The [[sudo]] command is similar but only allows for the running of a single command as root, and allows control over which users are allowed access to what commands.

== Provided by ==

Most (all?) Linux distributions incorporate this from the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils]: and use its man
[http://www.gnu.org/software/coreutils/manual/html_node/su-invocation.html page]

== Provided by ==
Most (all?) Linux distributions incorporate this from the [[https://www.kernel.org/pub/linux/utils/util-linux/ util-linux]] project.

== Related Commands ==
These all relate to running commands in an altered context.
* <tt>[[chroot]]</tt> - Confine the program to "jail".
* <tt>[[env(command)|env]]</tt> - Change variables.
* <tt>[[gdb]]</tt> - Run under control of a debugger
* <tt>[[nice]]</tt> - Change priority.
* <tt>[[nohup]]</tt> - Protect from hangups (modem) or network outages.
* <tt>[[runuser]]</tt> - Used by root to run a command as an ordinary user
* <tt>[[script]]</tt> - Capture all program output
* <tt>[[stdbuf]]</tt> - Change buffering of standard I/O filestreams.
* <tt>[[strace]]</tt> - Create a log of system calls.
* <tt>[[timeout]]</tt> - Limit the time.
* <tt>[[valgrind]]</tt> - Validate program behavior

==See also==
*[[security]]

{{stub}}

[[Category:Command]]

Dar

2020-07-20T16:55:04Z

4dummies: /* See Also */

'''dar''' is short for "disk archive". '''<tt>dar</tt>''' is both a [[command]] and a file format used by the command. It is used to collect several [[file]]s into one [[archive]], possibly split into several files (also known as "slices").

The official dar documentation refers to [[tar]] as its "grand-brother" and has a number of similarities, but dar implements features that were not possible when recording magnetic tapes, which was the original purpose of tar.
For instance, it uses a format that exploits the random-access capabilities of disk files for quicker access to individual files in the archive.

== Usage ==
dar [ -c | -t | -l | -x | -d | -* | -C ] [<path>/]<basename> [<options>] [<user targets>]
dar -h
dar -V

Unlike some other programs, "user targets" are not filenames but instead are names to be matched with configuration-file sections; these are a rich family of filters and other qualifiers that affect the way dar works. If the operation should not affect all files in the root (or the backup) this is done through options.

== About dar ==
Dar has several uses, but the most commonly used is to extract or to create dar archives.

It is specifically optimized for disk (or other seekable) archives, with a few distinctive features
* since the archives are seekable, selective extraction can be very fast.
* it is designed for archives that span volumes, in that archives are expected to comprise multiple "slices" and dar supports pauses to mount new volumes containing those slices.
* compression is applied to individual files, and may be suppressed for some file types.
* a "root" is used as a reference, and only files under that root are archived.

== Examples ==

To back up your home directory to a file (./myhome.1.dar) use either of

dar --create myhome --root ~ --exclude "myhome.*'
dar -c myhome -R ~ -X "myhome.*"

NOTES: the archive always decorates the name given with a slice number and ".dar". The exclusion is to prevent recursive archiving of the archive.

To back up specific files in your home directory (filename will be myfiles.1.dar) use either of

dar --create myfiles --root ~ --go-into file1 --go-into file2
dar -c myfiles -R ~ -g file1 -g file2

NOTES: in the absence of "<tt>--go-into</tt>" the entire root would be backed up.

== See Also ==
* [[ar]]
* [[cpio]]
* [[dar_cp]]
* [[dar_manager]]
* [[dar_slave]]
* [[dar_split]]
* [[dar_xform]]
* [[tar]]
* [[bzip2]]
* [[gzip]]
* [[partclone]]
* [[Packing and Unpacking Files]]

== External Links ==
* [http://dar.linux.free.fr/doc/index.html full official documentation]
* [http://dar.linux.free.fr/doc/man/dar.html man page]
* [http://dar.linux.free.fr/doc/Tutorial.html Tutorial]
{{stub}}

[[category:Command]]
[[category:Filehandling]]
[[Category:Application:Archive]]

Dar

2020-07-20T16:54:37Z

4dummies: /* See Also */

'''dar''' is short for "disk archive". '''<tt>dar</tt>''' is both a [[command]] and a file format used by the command. It is used to collect several [[file]]s into one [[archive]], possibly split into several files (also known as "slices").

The official dar documentation refers to [[tar]] as its "grand-brother" and has a number of similarities, but dar implements features that were not possible when recording magnetic tapes, which was the original purpose of tar.
For instance, it uses a format that exploits the random-access capabilities of disk files for quicker access to individual files in the archive.

== Usage ==
dar [ -c | -t | -l | -x | -d | -* | -C ] [<path>/]<basename> [<options>] [<user targets>]
dar -h
dar -V

Unlike some other programs, "user targets" are not filenames but instead are names to be matched with configuration-file sections; these are a rich family of filters and other qualifiers that affect the way dar works. If the operation should not affect all files in the root (or the backup) this is done through options.

== About dar ==
Dar has several uses, but the most commonly used is to extract or to create dar archives.

It is specifically optimized for disk (or other seekable) archives, with a few distinctive features
* since the archives are seekable, selective extraction can be very fast.
* it is designed for archives that span volumes, in that archives are expected to comprise multiple "slices" and dar supports pauses to mount new volumes containing those slices.
* compression is applied to individual files, and may be suppressed for some file types.
* a "root" is used as a reference, and only files under that root are archived.

== Examples ==

To back up your home directory to a file (./myhome.1.dar) use either of

dar --create myhome --root ~ --exclude "myhome.*'
dar -c myhome -R ~ -X "myhome.*"

NOTES: the archive always decorates the name given with a slice number and ".dar". The exclusion is to prevent recursive archiving of the archive.

To back up specific files in your home directory (filename will be myfiles.1.dar) use either of

dar --create myfiles --root ~ --go-into file1 --go-into file2
dar -c myfiles -R ~ -g file1 -g file2

NOTES: in the absence of "<tt>--go-into</tt>" the entire root would be backed up.

== See Also ==
* [[ar]]
* [[cpio]]
* [[dar_cp]]
* [[dar_manager]]
* [[dar_slave]]
* [[dar_split]]
* [[dar_xform]]
* [[tar]]
* [[bzip2]]
* [[dar]]
* [[gzip]]
* [[partclone]]
* [[Packing and Unpacking Files]]

== External Links ==
* [http://dar.linux.free.fr/doc/index.html full official documentation]
* [http://dar.linux.free.fr/doc/man/dar.html man page]
* [http://dar.linux.free.fr/doc/Tutorial.html Tutorial]
{{stub}}

[[category:Command]]
[[category:Filehandling]]
[[Category:Application:Archive]]

Partclone

2020-07-20T16:53:20Z

4dummies: /* See Also */

'''partclone''' refers to a family of command-line programs that copy the active blocks of a partition to or from a backup, or between partitions.

{{stub}}

= Variants =
The individual members of this family are:
* partclone.btrfs
* partclone.ext2, partclone.ext3, partclone.ext4 (all symbolic links to partclone.extfs)
* partclone.fat32, partclone.fat12, partclone.fat16 (all symbolic links to partclone.fat)
* partclone.ntfs
* partclone.exfat
* partclone.hfsplus (symbolic link to partclone.hfsp)
* partclone.jfs
* partclone.reiserfs
* partclone.reiser4
* partclone.ufs (with SU+J)
* partclone.vmfs (v3 and v5)
* partclone.xfs
* partclone.f2fs
* partclone.nilfs2
* partclone.dd (for unsupported filesystems -- it copies all blocks)

They are listed together because aside from the name and the kind of partition they handle, and almost all have the same command-line interface and options (partclone.dd is missing some options).

= See Also =
* [[partimage]]
* [[partclone.chkimg]]
* [[partclone.restore]]
* [[partclone.dd]]
* [[partclone.info]]
* [[partclone.ntfsfixboot]]
* [[ntfsclone]]
* [[dd]]
* [[tar]]
* [[ar]]
* [[bzip2]]
* [[dar]]
* [[gzip]]
* [[Packing and Unpacking Files]]

== External Links ==
* [https://sourceforge.net/projects/partclone/files/source/ Sourceforge repository]
* [https://partclone.org/ Partclone web site]
* [http://manpages.ubuntu.com/manpages/bionic/man8/partclone.8.html man page (Ubuntu bionic LTS)]

[[Category: Administrative commands]]
[[Category: Application:Archive]]

Partclone

2020-07-20T16:51:27Z

4dummies: /* Variants */

'''partclone''' refers to a family of command-line programs that copy the active blocks of a partition to or from a backup, or between partitions.

{{stub}}

= Variants =
The individual members of this family are:
* partclone.btrfs
* partclone.ext2, partclone.ext3, partclone.ext4 (all symbolic links to partclone.extfs)
* partclone.fat32, partclone.fat12, partclone.fat16 (all symbolic links to partclone.fat)
* partclone.ntfs
* partclone.exfat
* partclone.hfsplus (symbolic link to partclone.hfsp)
* partclone.jfs
* partclone.reiserfs
* partclone.reiser4
* partclone.ufs (with SU+J)
* partclone.vmfs (v3 and v5)
* partclone.xfs
* partclone.f2fs
* partclone.nilfs2
* partclone.dd (for unsupported filesystems -- it copies all blocks)

They are listed together because aside from the name and the kind of partition they handle, and almost all have the same command-line interface and options (partclone.dd is missing some options).

= See Also =
* [[partimage]]
* [[partclone.chkimg]]
* [[partclone.restore]]
* [[partclone.dd]]
* [[partclone.info]]
* [[partclone.ntfsfixboot]]
* [[ntfsclone]]
* [[dd]]
* [[tar]]

== External Links ==
* [https://sourceforge.net/projects/partclone/files/source/ Sourceforge repository]
* [https://partclone.org/ Partclone web site]
* [http://manpages.ubuntu.com/manpages/bionic/man8/partclone.8.html man page (Ubuntu bionic LTS)]

[[Category: Administrative commands]]
[[Category: Application:Archive]]

Tar

2020-07-20T16:50:02Z

4dummies: /* See also */ partclone

'''tar''' is short for "tape archive", although its use with magnetic tape backups is primarily of historical concern. '''<tt>tar</tt>''' is both a [[command]] and a file format used by the command. It is used to collect several [[file]]s into one [[archive]], which can be more easily managed or [[compression|compressed]] as a unit, often with [[gzip]] or [[bzip2]].

== Using tar==
Tar has several uses, but the most commonly used is to extract or to create tar archive (known as "tarballs")

=== .tar ===
To unpack a standard .tar file, use the command
tar -xvf ''filename''
The [[Command options]] of tar:
* ''x'': decompress something
* ''t'': view contents
* ''v'': [http://en.wikipedia.org/wiki/Verbose verbose] mode
* ''f'': input from a file

If the ''f'' flag is omitted, the command will read from [[stdin]]. This allows several interesting things: for example, [[pipe|piping]] output in tar format to tar, to have it untarred.

(Note that, unlike most commands, the '-' before the options may be omitted.)

To create a tarball, you can use
tar cf ''tarballname.tar'' ''files''
which can be compressed afterwards.

=== .tar.gz ===
Decompressing tarballs that have been gzipped can be done in two ways: first decompressing then extracting, by
[[gunzip]] ''filename''.tar.gz [[&&]] tar xf ''filename''.tar

Alternatively, some versions of tar support inbuilt decompression of [[gzip]]ped tar files. This requires the ''z'' option, transforming the command to:
tar -xvzf ''filename''

=== tar.bz2 ===
Decompressing [[Bzip2]] tar files can be done in the same manner, bunzip2 first and then tar, but some versions of tar allow you to use the ''j'' option:
tar -xvjf '''filename'''

If this option is not available to you, the same effect can be achieved by the following:
bunzip2 '''filename''' | tar -xvf -
where, as mentioned above, the output of bunzip2 is [[pipe]]d to tar, which is directed to read from stdin with the final '-'.

=== View contents of an archive ===
If you just want to view the contents of a tar file instead of extracting it:
tar -tf '''filename'''

You can filter it through gzip or bunzip2 respectively:
tar -tzf '''filename'''
tar -tjf '''filename'''

== Using tar to copy files ==
In addition to archiving files, tar can also be used to copy a group of files and directories using a [[pipe]]. To move all the files (including hidden ones) in /olddir to /newdir, for example, the syntax is
tar -c . | (cd /newdir; tar -xv)

Don't worry about the -v option with the pipe; the -v option writes to the [[stderr]] stream and will not interfere with the pipe.

== Using tar to transmit files ==
In addition to copying files, tar can also be used to transmit a group of files and directories using a [[pipe]] and [[ssh]]. To transmit all the files from your directory to the folder /archive on 192.168.0.80, for example, the syntax is
tar cv -f- . | ssh root@192.168.0.80 "(mkdir /archive; cd /archive; tar -xv)"
See also: [[Cloning]]

== Excluding Directories ==
Here's an example of including everything but ''opt'' and ''home'' directories.

tar --exclude=home --exclude=opt --exclude=srv -cvf slash.tar /

This excludes ''all'' ''opt'' and ''home'' directories, not just the ones under the [[current working directory]].

== Tar A Mounted Directory With No Leading Paths ==

tar -cvpjf /path/to/file.tar.bz2 ./*

This will tar any mounted directory and it will contain no nested path folders. This is helpful when you wish to back-up a mounted partition to a disk or another drive, and have the option of extracting it again without the usual leading paths.

== See also ==
* [[ar]]
* [[bzip2]]
* [[dar]]
* [[gzip]]
* [[Packing and Unpacking Files]]
* [[partclone]]

== External links ==
* [http://unixhelp.ed.ac.uk/CGI/man-cgi?tar tar man page]
* [http://www.debianhelp.co.uk/tarbackup.htm Taking backup Using tar Command]

[[category:Command]]
[[category:Filehandling]]
[[Category:Application:Archive]]

Sfdisk

2020-06-01T03:21:18Z

4dummies: added some 'sudo' to commands for consistency.

'''sfdisk''' is a non-GUI program to display and manipulate [[partition]]s in an [[MBR]] partition table on a [[hard drive]]. Since version 2.26, it also supports [[GPT Partition]]s, [[SUN Partition]]s and [[SGI Partition]]s.

==Examples==
===List sizes===
sudo sfdisk -s <partition>
will list the size of the partition in blocks. If no partition is named, all hard drives will be listed.

sudo sfdisk -s /dev/sda1
1024

===List partitions===
sudo sfdisk -l <device>
will list all partitions on the device, including missing ("empty") primary partitions.

sudo sfdisk -l /dev/sdj

Disk /dev/sdj: 243197 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/sdj1 0+ 243197- 243198- 1953480704 7 HPFS/NTFS/exFAT
/dev/sdj2 0 - 0 0 0 Empty
/dev/sdj3 0 - 0 0 0 Empty
/dev/sdj4 0 - 0 0 0 Empty

(note that the misalignment of Id and System columns above will happen on large drives)

===Check Partitions===
sudo sfdisk -V <device>
will perform checks on the partition table entries ('''not''' on the filesystems within those partitions).

===Create Partitions===
sudo sfdisk <device>
will read specification for a new partition from standard input. This is intended for use in a shell script.

===Other Uses===
There are enough other options for this command that the standard manual page lists ¨too many options" as a bug.

== Provided by ==
Most (all?) Linux distributions incorporate this from the [[https://www.kernel.org/pub/linux/utils/util-linux/ util-linux]] project.

==See also==
*[[cfdisk]]
*[[cgdisk]]
*[[fdisk]]
*[[fixparts]]
*[[gdisk]]
*[[gparted]]
*[[mkfs]]
*[[ntfsprogs]]
*[[parted]]
*[[partprobe]]
*[[partx]]
*[[sgdisk]]
*[[wipefs]]
*[[Partition]]
*[[GPT Partition]]
*[[Partitioning]]
*[[Partitioning guidelines]]

{{stub}}
[[Category:Administrative commands]]

Getfacl

2020-04-26T17:53:49Z

4dummies: /* See also */ add a link

'''getfacl''' is a file utility for viewing the [[access control list]] information associated with a file or directory.

Access control lists are extended attributes added to most major file systems in the 2.6 kernel to improve ability to control the access of files. They allow permissions to be set for individual groups and users and not just the owning user, owning group, and all other users.

= See also =
* [[lsattr]]
* [[setFacl]]
* [http://man-wiki.net/index.php/1:getfacl Getfacl Man page]

[[Category:filehandling]]
[[Category:command]]

Setfacl

2020-04-26T17:48:01Z

4dummies: Add a couple of examples and an internal see-also

'''setfacl''' is a command that allows you to set the [[Access Control List]] information for a file or directory.

Access control lists are extended attributes added to most major file systems in the 2.6 kernel to improve ability to control the access of files. They allow permissions to be set for individual groups and users and not just the owning user, owning group, and all other users.

{{stub}}
= Examples =

* Grant write access to an additional group ("them")
$ setfacl -m g:them:w file

* Remove a named user entry from the ACL
$ setfacl -m u:you file

= See also =
* [[getFacl]]
* [[chattr]]
* [http://man-wiki.net/index.php/1:setfacl setfacl man page]

[[category:command]]
[[category:filehandling]]

Setfacl

2020-04-26T16:38:15Z

4dummies: whitespace

'''setfacl''' is a command that allows you to set the [[Access Control List]] information for a file or directory.

Access control lists are extended attributes added to most major file systems in the 2.6 kernel to improve ability to control the access of files. They allow permissions to be set for individual groups and users and not just the owning user, owning group, and all other users.

{{stub}}

= See also =
* [[getFacl]]
* [http://man-wiki.net/index.php/1:setfacl setfacl man page]

[[category:command]]
[[category:filehandling]]

Dc

2019-12-24T16:46:41Z

4dummies: stubify

{{stub}}

'''dc''' is an arbitrary-precision reverse-polish calculator for the *NIX command line. It has a large number of operators, stacks and registers available.

$ dc
13 9 * p
27

== See Also ==
* [[bc]] A nornal-notation calculator, frequently (but not in GNU) implemented as a front-end to dc.

== External Links ==
* [https://www.gnu.org/software/bc/manual/dc-1.05/html_mono/dc.html dc's GNU man page]

* [https://en.wikipedia.org/wiki/Reverse_Polish_notation Wikipedia: reverse polish notation]

[[Category:Command]]

Bc

2019-12-24T16:45:29Z

4dummies: stubify

'''bc''' is a calculator for the console. It works like this:
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1+1
2
quit
$

By default, numbers are treated as integers, but you can set the number of fraction digits to retain and display by setting the variable '''scale''' like this:
scale=0
1/3
0
scale=5
1/3
.33333

As you might guess from this, you can assign values to other variables, and use them in calculations like this:
foo=1/3
foo*3
.99999

{{stub}}

== See also ==
* [[Console]]
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.
* <tt>[[seq]]</tt> - Show number sequences.

==External Links==
* [https://www.gnu.org/software/bc/manual/html_mono/bc.html bc's GNU man page]
* [http://man7.org/linux/man-pages/man1/bc.1p.html bc's POSIX man page]

[[Category:Command]]

Dc

2019-12-24T16:42:56Z

4dummies: /* External Links */ categorize

'''dc''' is an arbitrary-precision reverse-polish calculator for the *NIX command line. It has a large number of operators, stacks and registers available.

$ dc
13 9 * p
27

== See Also ==
* [[bc]] A nornal-notation calculator, frequently (but not in GNU) implemented as a front-end to dc.

== External Links ==
* [https://www.gnu.org/software/bc/manual/dc-1.05/html_mono/dc.html dc's GNU man page]

* [https://en.wikipedia.org/wiki/Reverse_Polish_notation Wikipedia: reverse polish notation]

[[Category:Command]]

Dc

2019-12-24T16:38:45Z

4dummies: /* External Links */ better link

Dc

2019-12-24T16:36:30Z

4dummies: /* External Links */

'''dc''' is an arbitrary-precision reverse-polish calculator for the *NIX command line. It has a large number of operators, stacks and registers available.

$ dc
13 9 * p
27

== See Also ==
* [[bc]] A nornal-notation calculator, frequently (but not in GNU) implemented as a front-end to dc.

== External Links ==
* [https://www.gnu.org/software/bc/manual/dc-1.05 dc's GNU man page]

* [https://en.wikipedia.org/wiki/Reverse_Polish_notation Wikipedia: reverse polish notation]

Dc

2019-12-24T16:35:20Z

4dummies: new page

'''dc''' is an arbitrary-precision reverse-polish calculator for the *NIX command line. It has a large number of operators, stacks and registers available.

$ dc
13 9 * p
27

== See Also ==
* [[bc]] A nornal-notation calculator, frequently (but not in GNU) implemented as a front-end to dc.

== External Links ==
* [https://www.gnu.org/software/bc/manual/html_mono/dc.html dc's GNU man page]

* [https://en.wikipedia.org/wiki/Reverse_Polish_notation Wikipedia: reverse polish notation]

Bc

2019-12-24T16:32:51Z

4dummies: /* External Links */

'''bc''' is a calculator for the console. It works like this:
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1+1
2
quit
$

By default, numbers are treated as integers, but you can set the number of fraction digits to retain and display by setting the variable '''scale''' like this:
scale=0
1/3
0
scale=5
1/3
.33333

As you might guess from this, you can assign values to other variables, and use them in calculations like this:
foo=1/3
foo*3
.99999

== See also ==
* [[Console]]
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.
* <tt>[[seq]]</tt> - Show number sequences.

==External Links==
* [https://www.gnu.org/software/bc/manual/html_mono/bc.html bc's GNU man page]
* [http://man7.org/linux/man-pages/man1/bc.1p.html bc's POSIX man page]

[[Category:Command]]

Bc

2019-12-24T16:29:25Z

4dummies: /* External Links */ fixed broken link, replaced by a GNU and a POSIX link

'''bc''' is a calculator for the console. It works like this:
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1+1
2
quit
$

By default, numbers are treated as integers, but you can set the number of fraction digits to retain and display by setting the variable '''scale''' like this:
scale=0
1/3
0
scale=5
1/3
.33333

As you might guess from this, you can assign values to other variables, and use them in calculations like this:
foo=1/3
foo*3
.99999

== See also ==
* [[Console]]
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.
* <tt>[[seq]]</tt> - Show number sequences.

==External Links==
* [https://www.gnu.org/software/bc/manual/html_mono/bc.html bc's GNU man page]
* [http://man7.org/linux/man-pages/man1/bc.1p.html bc/s POSIX man page]

[[Category:Command]]

Bc

2019-12-24T16:14:15Z

4dummies: a few more examples

'''bc''' is a calculator for the console. It works like this:
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1+1
2
quit
$

By default, numbers are treated as integers, but you can set the number of fraction digits to retain and display by setting the variable '''scale''' like this:
scale=0
1/3
0
scale=5
1/3
.33333

As you might guess from this, you can assign values to other variables, and use them in calculations like this:
foo=1/3
foo*3
.99999

== See also ==
* [[Console]]
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.
* <tt>[[seq]]</tt> - Show number sequences.

==External Links==
* [http://man-wiki.net/index.php/1:bc bc's man page]

[[Category:Command]]

Chmod

2019-12-24T16:07:57Z

4dummies: Undo revision 67002 by 4dummies (talk)

In Unix and Unix-like operating systems, a file has associated with it a number of security properties that control what the owner of the file and other users can do to the file. These properties are known as [[permissions]], and the '''<tt>chmod</tt>''' command modifies them.

== Permissions ==
Unix recognizes three groups of users who may want to access the file and bases the permissions accordingly. These groups are:
* the ''owner'' of the file (who created it)
* the ''group'' of that user - that is, other users who belong in the same group as the owner
* all other users.

These three groups are often abbreviated ''u'', ''g'', and ''o'' respectively.

Based on these three groups, a file can be
* readable - allow a file to be viewed
* writable - allow a file to be edited
* executable - allow a binary file to be run,
and are abbreviated ''r'', ''w'', and ''x'' respectively.

Other attributes for a file include a
* [[suid]] or [[sgid]] property, abbreviated ''s''
* a sticky bit, abbreviated ''t'' (seldom used)

== Notation ==
The <tt>chmod</tt> command can be used to set permissions on a directory or its files. However, how can we tell <tt>chmod</tt> how to apply the permissions?

Chmod accepts two notations, an alphabetic-based notation using the abbreviations mentioned above, and an [http://en.wikipedia.org/wiki/Octal octal], numeric based notation. It is possible to perform every operation using alphabetic notation as you can in octal, and vice versa. For new users, they may only need to learn the alphabetic notation.

=== Alphabetic notation ===
Say we want to set a file to have read and write access by the group the user is in. The notation for this permission is
g+rw

Or, say a file is set read-write-execute for all users, and we wish to limit the access to all other users, the permission is
o-rwx

In general, the permission is notated with the character of the user type first, + to set and - to clear, and then the characters representing the permissions to set.

===Numeric permissions===
Numeric permissions work by a group of octal numbers. Recall firstly that each digit in a hexadecimal number represents a block of 4 binary digits - similarly, for octal numbers, each digit represents a block of 3 binary digits.

Recall also that when a <tt>ls -l</tt> command is issued for a file, the permissions are listed in the form similar to
-rwxr-xr-x 1 yourusername yourgroup 19 Oct 22 09:25 yourfile

The permisssion list, <tt>-rwxr-xr-x</tt> is treated as a block of binary digits, a bitfield. Translating this into octal, we would get 0755, which is 0111101101 base 2.

We can then represent each permission for each user type by a single octal digit (plus an extra digit for the first bit).

* 400 <tt>-r--------</tt> read by owner
* 040 <tt>----r-----</tt> read by group
* 004 <tt>-------r--</tt> read by anybody (other)
* 200 <tt>--w-------</tt> write by owner
* 020 <tt>-----w----</tt> write by group
* 002 <tt>--------w-</tt> write by anybody
* 100 <tt>---x------</tt> execute by owner
* 010 <tt>------x---</tt> execute by group
* 001 <tt>---------x</tt> execute by anybody
* 4000 <tt>s---------</tt> suid
* 2000 <tt>s---------</tt> sgid
* 1000 <tt>t---------</tt> sticky

These permissions on their own may not be very useful, but we can add the octal numbers to get a combination of permissions. For example, 4, which corresponds to r-- (for some user type), and 2, which corresponds to -w- (for some user type), can be added to get 6, 110 in binary, which corresponds to rw-, read and write. Note also that in a group of three octal digits, the "place" of the digit signifies where we assign the permission. 600 octal, in binary is 0110000000, so we are setting read and write permissions for us, but not the group or other users. 060 octal, in binary however is 0000110000, and sets it for the group only, and likewise.

So, for example, if we want to set read and write for ourselves and the group, and have no permissions whatsoever for the other users, we could use the permission 660.

For the extra bit at the front, if the
fourth digit is omitted, chmod will leave the current setting. To clear the suid, sgid, and sticky bits, you must specify a 0 firstly to zero out the bit.

==Using chmod==
<tt>chmod</tt> is used by specifying the permissions, then the file to be operated on, for example:
chmod g+rwx filename
grants the group read/write/execute permissions to that file, or
chmod 755 filename
Writing 755 octal into binary would give us 0111101101, which translated into the usal permission notation would be -rwxr-xr-x, which gives all users the ability to read and execute the file, but neither the group nor any other users can write to the file.

<tt>chmod</tt> can be used to [http://simple.wikipedia.org/wiki/Recursion reCurse] down a directory tree - that is apply the same permissions to all files in a directory and its subdirectories by using the -R flag. For example,
chmod -R 755 *
sets all files in the current directory to the same permission above.

===Case study===
LTSP environment, students were able to view other students' work.

cd /home; chmod -R 750 *

Worked like a charm so that only owner can view and edit files.

= Provided by =

Most (all?) Linux distributions incorporate this from the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils]: man
[http://www.gnu.org/software/coreutils/manual/html_node/chmod-invocation.html page]

= Related Commands =
* [[chattr]]- Change attributes (Linux filesystems)
* [[chgrp]]- Changes group ownership of a file
* [[chown]]- Changes user/group ownership of a file
* [[ls]] - Lists files
* [[touch]] - update timestamps

==See also==
*[[Permissions]]

[[Category:Command]]
[[Category:Filehandling]]

Chmod

2019-12-24T16:06:43Z

4dummies: temporary

Userdel

2019-12-01T00:54:18Z

4dummies: /* See also */

[[userdel]] is a [[command]] to delete a [[user]]. It is a low-level utility, and should be avoided in favor of [[deluser]].

;Example:
userdel ''username''

= See also =
* [[adduser]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[groupmod]]
* [[adduser]]
* [[deluser]]
* [[passwd]]
* [[user commands]]
* [http://man-wiki.net/index.php/8:userdel userdel man page]

[[Category:Command]]

Userdel

2019-12-01T00:52:05Z

4dummies:

[[userdel]] is a [[command]] to delete a [[user]]. It is a low-level utility, and should be avoided in favor of [[deluser]].

;Example:
userdel ''username''

= See also =
* [[adduser]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[groupmod]]
* [[adduser]]
* [[deluser]]
* [[moduser]]
* [[passwd]]
* [[user commands]]
* [http://man-wiki.net/index.php/8:userdel userdel man page]

[[Category:Command]]

Userdel

2019-12-01T00:48:59Z

4dummies: /* See also */

[[userdel]] is a [[command]] to delete a [[user]].

;Example:
userdel ''username''

= See also =
* [[adduser]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[groupmod]]
* [[adduser]]
* [[deluser]]
* [[moduser]]
* [[passwd]]
* [[user commands]]
* [http://man-wiki.net/index.php/8:userdel userdel man page]

[[Category:Command]]

Userdel

2019-12-01T00:47:18Z

4dummies: /* See also */

[[userdel]] is a [[command]] to delete a [[user]].

;Example:
userdel ''username''

= See also =
* [[adduser]]
* [[userdel]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[groupmod]]
* [[useradd]]
* [[userdel]]
* [[usermod]]
* [[passwd]]
* [[user commands]]
* [http://man-wiki.net/index.php/8:userdel userdel man page]

[[Category:Command]]

Groupmod

2019-12-01T00:46:46Z

4dummies: /* See Also */

The [[command]] '''groupmod''' is used to modify a groupp.
((stub))

Be aware that the same capability is called '''groupmod''' on some systems and '''modgroup''' on others. This page describes the program found on Debian-based systems.

= Command line =

groupmod [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See also =
* [[adduser]]
* [[userdel]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[useradd]]
* [[userdel]]
* [[usermod]]
* [[passwd]]

[[Category:Command]]
[[Category:Administrative commands]]

Useradd

2019-12-01T00:46:16Z

4dummies: eliminate self-reference in see-also

The [[command]] '''useradd''' is used to create new [[user]]s to your [[Linux]] system. On [[Debian]], administrators should usually use the [[adduser]] command instead.

Using [http://en.wikipedia.org/wiki/Options options] to useradd you can specify a different placement for the users home directory for example. The option <tt>-D</tt> shows/sets the defaults for new users.

= Quickstart =
To add a user and set the password in a simple scenario (i.e. without home folders shared over different computers), [[open a console]] and enter:
useradd -m ''username''
passwd ''username''

= Command line options =

Specify the home directory:
-d home_dir

Create the home directory if it doesnt exit:
-m

Users Initial group:
-g initial_group

Add use to other groups:
-G group1,group2,etc

Select which shell they get:
-s shell

= Default Values =

To find out the default values that useradd will use, run:
$ useradd -D

= Specifying the Password =

== The Easy Way ==
Use the [[passwd]] command as [[root]]. By default passwd prompts for and changes the password of the user running it, but root can specify a different username as a command line argument and change that person's password.

Example of command to change the password for user Bob:
# passwd bob

== The Not So Easy Way ==
You can specify the password for the user using the -p option. The password must be specified with the output of the [http://man-wiki.net/index.php/3:crypt crypt] function.

[[Command line]] access to crypt is somewhat rare. The following C code generates an executable that will encrypt a password for you:

#include <stdio.h>
#include <unistd.h>
// compile with: g++ crypt.c -o crypt -lcrypt

int main(int argc, char** argv)
{
if( argc != 2 ) {
printf("usage: %s key-to-encrypt", argv[0]);
return 1;
}

printf("%s\n", crypt(argv[1], "01"));

return 0;
}

= See also =
* [[adduser]]
* [[userdel]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[groupmod]]
* [[userdel]]
* [[usermod]]
* [[passwd]]

[[Category:Command]]
[[Category:Administrative commands]]

Groupmod

2019-12-01T00:45:05Z

4dummies: warn about other names

The [[command]] '''groupmod''' is used to modify a groupp.
((stub))

Be aware that the same capability is called '''groupmod''' on some systems and '''modgroup''' on others. This page describes the program found on Debian-based systems.

= Command line =

groupmod [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See Also =
* [[useradd]]
* [[groupadd]]

[[Category:Command]]
[[Category:Administrative commands]]

Groupdel

2019-12-01T00:40:45Z

4dummies: see-alsos

The [[command]] '''groupdel''' is used to delete a group, changing the all records in the system account files to remove reference to the group.
((stub))

= Command line =

groupdel [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See Also =
* [[useradd]]
* [[groupadd]]
* [[groupmod]]

[[Category:Command]]
[[Category:Administrative commands]]

Useradd

2019-12-01T00:39:58Z

4dummies: more see-alsos

The [[command]] '''useradd''' is used to create new [[user]]s to your [[Linux]] system. On [[Debian]], administrators should usually use the [[adduser]] command instead.

Using [http://en.wikipedia.org/wiki/Options options] to useradd you can specify a different placement for the users home directory for example. The option <tt>-D</tt> shows/sets the defaults for new users.

= Quickstart =
To add a user and set the password in a simple scenario (i.e. without home folders shared over different computers), [[open a console]] and enter:
useradd -m ''username''
passwd ''username''

= Command line options =

Specify the home directory:
-d home_dir

Create the home directory if it doesnt exit:
-m

Users Initial group:
-g initial_group

Add use to other groups:
-G group1,group2,etc

Select which shell they get:
-s shell

= Default Values =

To find out the default values that useradd will use, run:
$ useradd -D

= Specifying the Password =

== The Easy Way ==
Use the [[passwd]] command as [[root]]. By default passwd prompts for and changes the password of the user running it, but root can specify a different username as a command line argument and change that person's password.

Example of command to change the password for user Bob:
# passwd bob

== The Not So Easy Way ==
You can specify the password for the user using the -p option. The password must be specified with the output of the [http://man-wiki.net/index.php/3:crypt crypt] function.

[[Command line]] access to crypt is somewhat rare. The following C code generates an executable that will encrypt a password for you:

#include <stdio.h>
#include <unistd.h>
// compile with: g++ crypt.c -o crypt -lcrypt

int main(int argc, char** argv)
{
if( argc != 2 ) {
printf("usage: %s key-to-encrypt", argv[0]);
return 1;
}

printf("%s\n", crypt(argv[1], "01"));

return 0;
}

= See also =
* [[adduser]]
* [[userdel]]
* [[usermod]]
* [[groupadd]]
* [[groupdel]]
* [[groupmod]]
* [[useradd]]
* [[userdel]]
* [[usermod]]
* [[passwd]]

[[Category:Command]]
[[Category:Administrative commands]]

Groupdel

2019-12-01T00:02:32Z

4dummies: /* See Also = */

The [[command]] '''groupdel''' is used to delete a group, changing the all records in the system account files to remove reference to the group.
((stub))

= Command line =

groupdel [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See Also =
* [[useradd]]
* [[groupadd]]

[[Category:Command]]
[[Category:Administrative commands]]

Groupadd

2019-12-01T00:02:10Z

4dummies: /* See Also */

'''Groupadd''' is a [[command]] in [[Linux]] to create a new [[group]] for [[user]] administration.

This command can be used, or the [[superuser]] can edit the group configuration file <tt>/etc/group</tt> with [[vigr]].

== See Also ==
* [[groupdel]]

[[Category:Command]]
[[Category:Administrative commands]]
{{stub}}

Groupadd

2019-12-01T00:01:43Z

4dummies: see also groupadd

'''Groupadd''' is a [[command]] in [[Linux]] to create a new [[group]] for [[user]] administration.

This command can be used, or the [[superuser]] can edit the group configuration file <tt>/etc/group</tt> with [[vigr]].

== See Also ==
* groupdel

[[Category:Command]]
[[Category:Administrative commands]]
{{stub}}

Groupadd

2019-12-01T00:00:49Z

4dummies: category

'''Groupadd''' is a [[command]] in [[Linux]] to create a new [[group]] for [[user]] administration.

This command can be used, or the [[superuser]] can edit the group configuration file <tt>/etc/group</tt> with [[vigr]].

[[Category:Command]]
[[Category:Administrative commands]]
{{stub}}

Groupdel

2019-12-01T00:00:21Z

4dummies: change categories

The [[command]] '''groupdel''' is used to delete a group, changing the all records in the system account files to remove reference to the group.
((stub))

= Command line =

groupdel [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See Also ==
* [[useradd]]
* [[groupadd]]

[[Category:Command]]
[[Category:Administrative commands]]

Groupadd

2019-11-30T23:56:50Z

4dummies: it's only a stub

Groupadd

2019-11-30T23:56:25Z

4dummies: made administrative

Groupdel

2019-11-30T23:55:42Z

4dummies: Make administrative

The [[command]] '''groupdel''' is used to delete a group, changing the all records in the system account files to remove reference to the group.
((stub))

= Command line =

groupdel [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See Also ==
* [[useradd]]
* [[groupadd]]

[[Category: Administrative commands]]

Groupdel

2019-11-30T23:54:34Z

4dummies: Satisfy a reference in the commands list

The [[command]] '''groupdel''' is used to delete a group, changing the all records in the system account files to remove reference to the group.
((stub))

= Command line =

groupdel [options] group

= Options =

-h --help Display help message
-R --root CHROOT_DIR apply changes in the CHROOT_DIR

= See Also ==
* [[useradd]]
* [[groupadd]]

[[Category: Command]]

Factor

2019-09-20T00:19:32Z

4dummies: /* Related Commands */

The '''factor''' command shows the prime factors of a positive integer. The program can handle numbers up to 18446744073709551615 (2^64 - 1) on a 32-bit machine, or 170141183460469231731687303715884105727 (2^127-1) on a 64-bit machine.

== Examples ==

On a 32-bit machine
$ factor 1920 1080
1920: 2 2 2 2 2 2 2 3 5
1080: 2 2 2 3 3 3 5

$ factor 18446744073709551616
factor: `18446744073709551616' is too large
$ factor 18446744073709551615 '''(the largest number it can process on a 32-bit machine)'''
18446744073709551615: 3 5 17 257 641 65537 6700417
$ factor 18446744073709551557
18446744073709551557: 18446744073709551557 '''(the largest prime it can verify on a 32-bit machine)'''

On a 64-bit machine
$ factor 170141183460469231731687303715884105727
170141183460469231731687303715884105727: 170141183460469231731687303715884105727 '''(the largest number it can process on a 64-bit machine is prime)
$ factor 170141183460469231731687303715884105697
170141183460469231731687303715884105697: 4347014963 39139774053837143815620977819

== Speed ==

The coreutils version uses sophisticated number theory methods to speed things up, especially when all factors are small. Prime numbers are detected effectively instantaneously, but composite numbers with more than one large factor can take significant time to process. For instance, Xubuntu on a 4 GHz Core i7 shows

$ time factor $(echo 2^127-1 | bc) # A prime number -- very fast
170141183460469231731687303715884105727: 170141183460469231731687303715884105727
real 0m0.005s
user 0m0.006s
sys 0m0.001s

$ time factor $(echo 2^127-305 | bc) # A slightly smaller composite with 2 large factors - 2 minutes
170141183460469231731687303715884105423: 3 6490505778597245129 8737951980132681629
real 2m1.311s
user 2m1.300s
sys 0m0.000s

$ time factor $(echo 10^38+231 | bc) # A somewhat smaller composite but with larger factors - 2.5 minutes
100000000000000000000000000000000000231: 9232227618290977207 10831622023906673233
real 2m31.258s
user 2m31.248s
sys 0m0.008s

== Provided by ==
This command occurs in the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] where a man
[http://www.gnu.org/software/coreutils/manual/html_node/factor-invocation.html page] can also be found. Many Linux systems, however, are using a different version. The current author has not yet tracked this down.

== Related Commands ==
* <tt>[[bc]]</tt> - arbitrary precision calculator language
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[seq]]</tt> - Show number sequences.

[[Category:Command]]

Bc

2019-09-20T00:18:44Z

4dummies: /* See also */

'''bc''' is a calculator for the console. It works like this:
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1+1
2
quit
$
== See also ==
* [[Console]]
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.
* <tt>[[seq]]</tt> - Show number sequences.

==External Links==
* [http://man-wiki.net/index.php/1:bc bc's man page]

[[Category:Command]]

Factor

2019-09-20T00:17:32Z

4dummies: /* Related Commands */

The '''factor''' command shows the prime factors of a positive integer. The program can handle numbers up to 18446744073709551615 (2^64 - 1) on a 32-bit machine, or 170141183460469231731687303715884105727 (2^127-1) on a 64-bit machine.

== Examples ==

On a 32-bit machine
$ factor 1920 1080
1920: 2 2 2 2 2 2 2 3 5
1080: 2 2 2 3 3 3 5

$ factor 18446744073709551616
factor: `18446744073709551616' is too large
$ factor 18446744073709551615 '''(the largest number it can process on a 32-bit machine)'''
18446744073709551615: 3 5 17 257 641 65537 6700417
$ factor 18446744073709551557
18446744073709551557: 18446744073709551557 '''(the largest prime it can verify on a 32-bit machine)'''

On a 64-bit machine
$ factor 170141183460469231731687303715884105727
170141183460469231731687303715884105727: 170141183460469231731687303715884105727 '''(the largest number it can process on a 64-bit machine is prime)
$ factor 170141183460469231731687303715884105697
170141183460469231731687303715884105697: 4347014963 39139774053837143815620977819

== Speed ==

The coreutils version uses sophisticated number theory methods to speed things up, especially when all factors are small. Prime numbers are detected effectively instantaneously, but composite numbers with more than one large factor can take significant time to process. For instance, Xubuntu on a 4 GHz Core i7 shows

$ time factor $(echo 2^127-1 | bc) # A prime number -- very fast
170141183460469231731687303715884105727: 170141183460469231731687303715884105727
real 0m0.005s
user 0m0.006s
sys 0m0.001s

$ time factor $(echo 2^127-305 | bc) # A slightly smaller composite with 2 large factors - 2 minutes
170141183460469231731687303715884105423: 3 6490505778597245129 8737951980132681629
real 2m1.311s
user 2m1.300s
sys 0m0.000s

$ time factor $(echo 10^38+231 | bc) # A somewhat smaller composite but with larger factors - 2.5 minutes
100000000000000000000000000000000000231: 9232227618290977207 10831622023906673233
real 2m31.258s
user 2m31.248s
sys 0m0.008s

== Provided by ==
This command occurs in the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] where a man
[http://www.gnu.org/software/coreutils/manual/html_node/factor-invocation.html page] can also be found. Many Linux systems, however, are using a different version. The current author has not yet tracked this down.

== Related Commands ==
* <tt>[[bc]]</tt> - arbitrary precision calculator language
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.
* <tt>[[seq]]</tt> - Show number sequences.

[[Category:Command]]

Seq

2019-09-20T00:16:36Z

4dummies: /* Related Commands */

The '''seq''' command shows arithmetic sequences.

= Usage =
For the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] version:
seq [OPTION]... [FIRST [INCREMENT]] LAST

= Options =
-f --format=FORMAT uses the same syntax as [[printf]]
-s --separator=STRING (defaults to \n)
-w --equal-width pads output with leading zeroes

= Examples =
[[seq]] -s "" 10
12345678910

[[seq]] -ws ' ' 2 10
02 03 04 05 06 07 08 09 10

[[seq]] .5 -1 -2
0.5
-0.5
-1.5

= Provided by =
This command occurs in the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] where a man
[http://www.gnu.org/software/coreutils/manual/html_node/seq-invocation.html page] can also be found. Many Linux systems, however, are using a different version. The current author has not yet tracked this down.

Later: as Ubuntu (and probably debian) uses the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] version, the options and examples are for that version.

= Related Commands =
These all relate to numeric operations
* <tt>[[bc]]</tt> - arbitrary precision calculator language
* <tt>[[dc]]</tt> - reverse-polish arbitrary precision calculator
* <tt>[[factor]]</tt> - Factor positive integers.

[[Category:Command]]

Factor

2019-09-18T20:01:49Z

4dummies: details

The '''factor''' command shows the prime factors of a positive integer. The program can handle numbers up to 18446744073709551615 (2^64 - 1) on a 32-bit machine, or 170141183460469231731687303715884105727 (2^127-1) on a 64-bit machine.

== Examples ==

On a 32-bit machine
$ factor 1920 1080
1920: 2 2 2 2 2 2 2 3 5
1080: 2 2 2 3 3 3 5

$ factor 18446744073709551616
factor: `18446744073709551616' is too large
$ factor 18446744073709551615 '''(the largest number it can process on a 32-bit machine)'''
18446744073709551615: 3 5 17 257 641 65537 6700417
$ factor 18446744073709551557
18446744073709551557: 18446744073709551557 '''(the largest prime it can verify on a 32-bit machine)'''

On a 64-bit machine
$ factor 170141183460469231731687303715884105727
170141183460469231731687303715884105727: 170141183460469231731687303715884105727 '''(the largest number it can process on a 64-bit machine is prime)
$ factor 170141183460469231731687303715884105697
170141183460469231731687303715884105697: 4347014963 39139774053837143815620977819

== Speed ==

The coreutils version uses sophisticated number theory methods to speed things up, especially when all factors are small. Prime numbers are detected effectively instantaneously, but composite numbers with more than one large factor can take significant time to process. For instance, Xubuntu on a 4 GHz Core i7 shows

$ time factor $(echo 2^127-1 | bc) # A prime number -- very fast
170141183460469231731687303715884105727: 170141183460469231731687303715884105727
real 0m0.005s
user 0m0.006s
sys 0m0.001s

$ time factor $(echo 2^127-305 | bc) # A slightly smaller composite with 2 large factors - 2 minutes
170141183460469231731687303715884105423: 3 6490505778597245129 8737951980132681629
real 2m1.311s
user 2m1.300s
sys 0m0.000s

$ time factor $(echo 10^38+231 | bc) # A somewhat smaller composite but with larger factors - 2.5 minutes
100000000000000000000000000000000000231: 9232227618290977207 10831622023906673233
real 2m31.258s
user 2m31.248s
sys 0m0.008s

== Provided by ==
This command occurs in the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] where a man
[http://www.gnu.org/software/coreutils/manual/html_node/factor-invocation.html page] can also be found. Many Linux systems, however, are using a different version. The current author has not yet tracked this down.

== Related Commands ==
* [[bc]] - a calculator
* [[seq]] - Show number sequences.

[[Category:Command]]

Factor

2019-09-18T19:55:18Z

4dummies: Add some speed info

The '''factor''' command shows the prime factors of a positive integer. The program can handle numbers up to 18446744073709551615 (2^64 - 1) on a 32-bit machine, or 170141183460469231731687303715884105727 (2^127-1) on a 64-bit machine.

== Examples ==

On a 32-bit machine
$ factor 1920 1080
1920: 2 2 2 2 2 2 2 3 5
1080: 2 2 2 3 3 3 5

$ factor 18446744073709551616
factor: `18446744073709551616' is too large
$ factor 18446744073709551615 '''(the largest number it can process on a 32-bit machine)'''
18446744073709551615: 3 5 17 257 641 65537 6700417
$ factor 18446744073709551557
18446744073709551557: 18446744073709551557 '''(the largest prime it can verify on a 32-bit machine)'''

On a 64-bit machine
$ factor 170141183460469231731687303715884105727
170141183460469231731687303715884105727: 170141183460469231731687303715884105727 '''(the largest number it can process on a 64-bit machine is prime)
$ factor 170141183460469231731687303715884105697
170141183460469231731687303715884105697: 4347014963 39139774053837143815620977819

== Speed ==

The coreutils version uses sophisticated number theory methods to speed things up, especially when all factors are small. Prime numbers are detected effectively instantaneously, but composite numbers with more than one large factor can take significant time to process. For instance, on a 4 GHz Core i7,

$ time factor $(echo 2^127-1 | bc) # A prime number -- very fast
170141183460469231731687303715884105727: 170141183460469231731687303715884105727
real 0m0.005s
user 0m0.006s
sys 0m0.001s

$ time factor $(echo 2^127-305 | bc) # A slightly smaller composite with 2 large factors - 2 minutes
170141183460469231731687303715884105423: 3 6490505778597245129 8737951980132681629
real 2m1.311s
user 2m1.300s
sys 0m0.000s

$ time factor $(echo 10^38+231 | bc) # A somewhat smaller composite but with larger factors - 2.5 minutes
100000000000000000000000000000000000231: 9232227618290977207 10831622023906673233
real 2m31.258s
user 2m31.248s
sys 0m0.008s

== Provided by ==
This command occurs in the [http://www.gnu.org/software/coreutils/manual/html_node/index.html#Top GNU Coreutils] where a man
[http://www.gnu.org/software/coreutils/manual/html_node/factor-invocation.html page] can also be found. Many Linux systems, however, are using a different version. The current author has not yet tracked this down.

== Related Commands ==
* [[bc]] - a calculator
* [[seq]] - Show number sequences.

[[Category:Command]]

Cut

2019-09-18T19:30:58Z

4dummies: /* See Also */ formatting

= cut =

The <tt>cut</tt> command is a handy program for extracting pieces of a line of text.
The most useful options are "-d" and "-f", which are for setting the "delimiter" character that separates items, and for telling Cut which "fields" you want it to print.

For example, let's say you have the following line of text, and you only want the 3rd and 6th columns:
:''foo,bar,baz,stuff,blah,oogabooga''
you could run it through this cut command:
cut -d',' -f 3,6
and the output would be:
baz,oogabooga

== A more practical example ==
Perhaps you want to take the output of ''ls -l'' but only see the permissions, size, and name of the files.<br>
Here is some sample output of ''ls -l'':<Br>
-rw-r--r-- 1 pete users 65767 Mar 5 17:36 school.pdf
-rw------- 1 pete users 34552 Mar 5 17:36 soup.jpg
-rw-rw-r-- 1 pete users 63 Mar 5 17:36 taxes.txt

First, here's a trick to use [[tr]] to squeeze multiple spaces into just one space:<Br>
$ ls -l | tr -s ' '
-rw-r--r-- 1 pete users 65767 Mar 5 17:36 school.pdf
-rw------- 1 pete users 34552 Mar 5 17:36 soup.jpg
-rw-rw-r-- 1 pete users 63 Mar 5 17:36 taxes.txt

And now, here's how to use cut to chop it into bits based on the spaces as a delimiter:<br>
$ ls -l | tr -s ' ' | cut -d' ' -f 1,5,9
-rw-r--r-- 65767 school.pdf
-rw------- 34552 soup.jpg
-rw-rw-r-- 63 taxes.txt

= See Also =
*[[paste]]
*[[join]]

[[Category:Command]]

Shebang

2019-08-04T17:51:30Z

4dummies: Link to additional info

'''shebang''' sometimes also called '''hashbang''' is the common name for the sequence of characters used at the start of a [[shell script]], taking the form of a hash followed by an exclamation mark:

#!

The name derives from the "sh" sound at the end of "hash", plus "bang" which is a short name for the exclamation mark.

When used in a shell script the hash symbol typically denotes the beginning of a [[comment]]. However in the particular case of the shebang sequence occurring as the first two characters of a file, the running [[shell]] will treat the rest of first line as a path to the [[interpreter]] required to execute the script. For instance:

<pre>
#!/usr/bin/perl

#!/usr/local/bin/bash

#!/bin/sh

#!/bin/awk -f
</pre>
== See also ==
[[Env(command)]] -- see the special trick section

[[Category:Concept]]

Chattr

2019-08-04T16:44:44Z

4dummies: /* See also */ see also to 'chmod'

[[chattr]] is a [[command]] used to set the [[file]] attributes.

== Description ==

The format of a symbolic mode is +-=[ASacDdIijsTtu].

The operator ‘+’ causes the selected attributes to be added to the existing attributes of the files; ‘-’ causes them to be removed; and ‘=’ causes them to be the only attributes that the files have.

The letters ‘acdijsuADST’ select the new attributes for the files:

* '''a'''ppend only: File can be opened only in append mode
* '''c'''ompressed: The file on the disk is automatically compressed. If read is performed from this file, uncompressed data is returned. If write is performed on this file, data is compressed before being written
* no '''d'''ump
* '''i'''mmutable: The file cannot be modified,
* data '''j'''ournalling
* '''s'''ecure deletion
* no '''t'''ail-merging
* '''u'''ndeletable: When such a file is deleted, its contents are saved. So it can be undeleted.
* no '''A'''time updates
* synchronous '''D'''irectory updates
* '''S'''ynchronous updates
* '''T'''op of directory hierarchy

View the [http://man-wiki.net/index.php/1:chattr man page] for more details.

== See also ==
* [[chmod]]
* [[lsattr]]

[[Category:Command]]
[[Category:Administrative commands]]

Chmod

2019-08-04T16:43:29Z

4dummies: /* Related Commands */ added 'chattr'

Wipefs

2019-06-04T18:59:51Z

4dummies: link to testdisk

'''wipefs''' reports signatures of filesystems or devices, or wipes them out so that they are invisible to libblkid and thus to the blkid program.

== Provided by ==
Most (all?) Linux distributions incorporate this from the [[https://www.kernel.org/pub/linux/utils/util-linux/ util-linux]] project.

==See also==
Programs:
*[[blkid]]
*[[cfdisk]]
*[[cgdisk]]
*[[fdisk]]
*[[findfs]]
*[[fixparts]]
*[[gdisk]]
*[[gparted]]
*[[mkfs]]
*[[ntfsprogs]]
*[[parted]]
*[[partprobe]]
*[[partx]]
*[[sfdisk]]
*[[sgdisk]]
*[[testdisk]]

Concepts:
*[[Partition]]
*[[GPT Partition]]
*[[Partitioning]]
*[[Partitioning guidelines]]

* [https://fossies.org/linux/util-linux/disk-utils/wipefs.8 man page]

{{stub}}
[[Category:Administrative commands]]