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feat: Add install command to chapter 4 "advanced" command #1630

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142 changes: 109 additions & 33 deletions docs/books/admin_guide/04-advanced-commands.md
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
---
title: Advanced Linux Commands
title: Advanced Commands for Linux users
---
<!-- markdownlint-disable MD033 -->

# Advanced Commands for Linux users

Expand All @@ -10,12 +11,12 @@ Advanced commands provide greater customization and controls in more specialized

**Objectives**: In this chapter, future Linux administrators will learn:

:heavy_check_mark: some useful commands not covered in the previous chapter.
:heavy_check_mark: some useful commands not covered in the previous chapter.
:heavy_check_mark: some advanced commands.

:checkered_flag: **user commands**, **Linux**

**Knowledge**: :star:
**Knowledge**: :star:
**Complexity**: :star: :star: :star:

**Reading time**: 20 minutes
Expand All @@ -28,7 +29,7 @@ The `uniq` command is a very powerful command, used with the `sort` command, esp

To illustrate how the `uniq` command works, let's use a `firstnames.txt` file containing a list of first names:

```
```text
antoine
xavier
steven
Expand All @@ -45,7 +46,7 @@ steven

With no argument, the `uniq` command will not display identical lines that follow each other in the `firstnames.txt` file:

```
```bash
$ sort firstnames.txt | uniq
antoine
patrick
Expand All @@ -55,14 +56,14 @@ xavier

To display only the rows that appear only once, use the `-u` option:

```
```bash
$ sort firstnames.txt | uniq -u
patrick
```

Conversely, to display only the lines that appear at least twice in the file, use the `-d` option:

```
```bash
$ sort firstnames.txt | uniq -d
antoine
steven
Expand All @@ -71,7 +72,7 @@ xavier

To simply delete lines that appear only once, use the `-D` option:

```
```bash
$ sort firstnames.txt | uniq -D
antoine
antoine
Expand All @@ -84,15 +85,15 @@ xavier

Finally, to count the number of occurrences of each line, use the `-c` option:

```
```bash
$ sort firstnames.txt | uniq -c
3 antoine
1 patrick
2 steven
2 xavier
```

```
```bash
$ sort firstnames.txt | uniq -cd
3 antoine
2 steven
Expand All @@ -107,7 +108,7 @@ The `xargs` command reads whitespace or linefeed delimited arguments from standa

A first and simplest example would be the following:

```
```bash
$ xargs
use
of
Expand All @@ -118,7 +119,7 @@ use of xargs

The `xargs` command waits for an input from the standard **stdin** input. Three lines are entered. The end of the user input is specified to `xargs` by the keystroke sequence <kbd>CTRL</kbd>+<kbd>D</kbd>. `xargs` then executes the default command `echo` followed by the three arguments corresponding to the user input, namely:

```
```bash
$ echo "use" "of" "xargs"
use of xargs
```
Expand All @@ -127,7 +128,7 @@ It is possible to specify a command to be run by `xargs`.

In the following example, `xargs` will run the command `ls -ld` on the set of folders specified in the standard input:

```
```bash
$ xargs ls -ld
/home
/tmp
Expand All @@ -142,7 +143,7 @@ In practice, the `xargs` command executed the `ls -ld /home /tmp /root` command.

What happens if the command to be executed does not accept multiple arguments, such as with the `find` command?

```
```bash
$ xargs find /var/log -name
*.old
*.log
Expand All @@ -151,14 +152,14 @@ find: paths must precede expression: *.log

The `xargs` command attempted to execute the `find` command with multiple arguments behind the `-name` option, which caused `find` to generate an error:

```
```bash
$ find /var/log -name "*.old" "*.log"
find: paths must precede expression: *.log
```

In this case, the `xargs` command must be forced to execute the `find` command several times (once per line entered as standard input). The `-L` option followed by an **integer** allows you to specify the maximum number of entries to be processed with the command at one time:

```
```bash
$ xargs -L 1 find /var/log -name
*.old
/var/log/dmesg.old
Expand All @@ -177,7 +178,7 @@ $ xargs -L 1 find /var/log -name

To specify both arguments on the same line, use the `-n 1` option:

```
```bash
$ xargs -n 1 find /var/log -name
*.old *.log
/var/log/dmesg.old
Expand All @@ -195,7 +196,7 @@ $ xargs -n 1 find /var/log -name

Case study of a backup with a `tar` based on a search:

```
```bash
$ find /var/log/ -name "*.log" -mtime -1 | xargs tar cvfP /root/log.tar
$ tar tvfP /root/log.tar
-rw-r--r-- root/root 1720 2017-04-05 15:43 /var/log/boot.log
Expand All @@ -206,8 +207,8 @@ The special feature of the `xargs` command is that it places the input argument

Using the example of the `cp` command, to copy a list of files in a directory, this list of files will be added at the end of the command... but what the `cp` command expects at the end of the command is the destination. To do this, use the `-I` option to put the input arguments somewhere else than at the end of the line.

```
$ find /var/log -type f -name "*.log" | xargs -I % cp % /root/backup
```bash
find /var/log -type f -name "*.log" | xargs -I % cp % /root/backup
```

The `-I` option allows you to specify a character (the `%` character in the above example) where the input files to `xargs` will be placed.
Expand All @@ -229,13 +230,14 @@ The `repoquery` command is used to query the packages in the repository.
Examples of use:

* Display the dependencies of a package (it can be a software package that has been installed or not installed), equivalent to `dnf deplist <package-name>`
```

```bash
repoquery --requires <package-name>
```

* Display the files provided by an installed package (does not work for packages that are not installed), equivalent to `rpm -ql <package-name>`

```
```bash
$ repoquery -l yum-utils
/etc/bash_completion.d
/etc/bash_completion.d/yum-utils.bash
Expand Down Expand Up @@ -273,7 +275,7 @@ The `yumdownloader` command downloads RPM packages from the repositories. Equiv

Example: `yumdownloader` will download the _samba_ rpm package and all its dependencies:

```
```bash
$ yumdownloader --destdir /var/tmp --resolve samba
or
$ dnf download --downloadonly --downloaddir /var/tmp --resolve samba
Expand All @@ -294,7 +296,7 @@ The `psmisc` package contains utilities for managing system processes:

Examples:

```
```bash
$ pstree
systemd─┬─NetworkManager───2*[{NetworkManager}]
├─agetty
Expand All @@ -314,13 +316,13 @@ systemd─┬─NetworkManager───2*[{NetworkManager}]
└─tuned───4*[{tuned}]
```

```
```bash
# killall httpd
```

Kill processes (option `-k`) that access the `/etc/httpd/conf/httpd.conf` file:

```
```bash
# fuser -k /etc/httpd/conf/httpd.conf
```

Expand All @@ -338,13 +340,13 @@ Examples:

* Display the end of the `/etc/passwd` file every 5 seconds:

```
$ watch -n 5 tail -n 3 /etc/passwd
```bash
watch -n 5 tail -n 3 /etc/passwd
```

Result:

```
```bash
Every 5.0s: tail -n 3 /etc/passwd rockstar.rockylinux.lan: Thu Jul 1 15:43:59 2021

sssd:x:996:993:User for sssd:/:/sbin/nologin
Expand All @@ -354,12 +356,86 @@ sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin

* Monitoring the number of files in a folder:

```
$ watch -n 1 'ls -l | wc -l'
```bash
watch -n 1 'ls -l | wc -l'
```

* Display a clock:

```bash
watch -t -n 1 date
```

## `install` command

Contrary to what its name might suggest, the `install` command is not used to install new packages.

This command combines file copying (`cp`) and directory creation (`mkdir`), with rights management (`chmod`, `chown`) and other useful functionalities (like backups).

```bash
install source dest
install -t directory source [...]
install -d directory
```

Options:

| Options | Remarks                           |
| ------- | ------------------------------------------------------------ |
| `-b` or `--backup[=suffix]` | create a backup of destination file. |
| `-d`    | treat arguments as directory names.               |
| `-D`    | create all leading components before copying SOURCE to DEST. |
| `-g` and `-o`    | set ownership.               |
| `-m`    | set permissions.               |
| `-p`    | preserve the timestamps of sources files.               |
| `-t` | copy all source arguments to directory. |

!!! NOTE
There are options for managing the SELinux context (see the manual page).

Examples:

Create a directory with the `-d` option:

```bash
install -d ~/samples
```

Copy a file from a source location to a directory:

```bash
install src/sample.txt ~/samples/
```

These two orders could have been carried out with a single command:

```bash
$ install -v -D -t ~/samples/ src/sample.txt
install: creating directory '~/samples'
'src/sample.txt' -> '~/samples/sample.txt'
```

This command already saves time, now let's combine it with owner, owner group and rights management:

```bash
sudo install -v -o rocky -g users -m 644 -D -t ~/samples/ src/sample.txt
```
$ watch -t -n 1 date

!!! NOTE
`sudo` is required in this case to make property changes.

You can also create a backup of existing files thanks to the `-b` option:

```bash
$ install -v -b -D -t ~/samples/ src/sample.txt
'src/sample.txt' -> '~/samples/sample.txt' (archive: '~/samples/sample.txt~')
```

As you can see, the `install` command creates a backup file with a `~` tilde appended to the original file name.

The suffix can be specified thanks to the `-S` option:

```bash
$ install -v -b -S ".bak" -D -t ~/samples/ src/sample.txt
'src/sample.txt' -> '~/samples/sample.txt' (archive: '~/samples/sample.txt.bak')
```