TranslateProject/sources/tech/20150911 5 Useful Commands to Manage File Types and System Time in Linu--Part 3.md

5 Useful Commands to Manage File Types and System Time in Linux – Part 3
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Adapting to using the command line or terminal can be very hard for beginners who want to learn Linux. Because the terminal gives more control over a Linux system than GUIs programs, one has to get a used to running commands on the terminal. Therefore to memorize different commands in Linux, you should use the terminal on a daily basis to understand how commands are used with different options and arguments.

![Manage File Types and Set Time in Linux](http://www.tecmint.com/wp-content/uploads/2015/09/Find-File-Types-in-Linux.jpg)

Manage File Types and Set Time in Linux – Part 3

Please go through our previous parts of this [Linux Tricks][1] series.

- [5 Interesting Command Line Tips and Tricks in Linux – Part 1][2]
- [ Useful Commandline Tricks for Newbies – Part 2][3]

In this article, we are going to look at some tips and tricks of using 10 commands to work with files and time on the terminal.

### File Types in Linux ###

In Linux, everything is considered as a file, your devices, directories and regular files are all considered as files.

There are different types of files in a Linux system:

- Regular files which may include commands, documents, music files, movies, images, archives and so on.
- Device files: which are used by the system to access your hardware components.

There are two types of device files block files that represent storage devices such as harddisks, they read data in blocks and character files read data in a character by character manner.

- Hardlinks and softlinks: they are used to access files from any where on a Linux filesystem.
- Named pipes and sockets: allow different processes to communicate with each other.

#### 1. Determining the type of a file using ‘file’ command ####

You can determine the type of a file by using the file command as follows. The screenshot below shows different examples of using the file command to determine the types of different files.

    tecmint@tecmint ~/Linux-Tricks $ dir
    BACKUP				      master.zip
    crossroads-stable.tar.gz	      num.txt
    EDWARD-MAYA-2011-2012-NEW-REMIX.mp3   reggea.xspf
    Linux-Security-Optimization-Book.gif  tmp-link
    
    tecmint@tecmint ~/Linux-Tricks $ file BACKUP/
    BACKUP/: directory 
    
    tecmint@tecmint ~/Linux-Tricks $ file master.zip 
    master.zip: Zip archive data, at least v1.0 to extract
    
    tecmint@tecmint ~/Linux-Tricks $ file crossroads-stable.tar.gz
    crossroads-stable.tar.gz: gzip compressed data, from Unix, last modified: Tue Apr  5 15:15:20 2011
    
    tecmint@tecmint ~/Linux-Tricks $ file Linux-Security-Optimization-Book.gif 
    Linux-Security-Optimization-Book.gif: GIF image data, version 89a, 200 x 259
    
    tecmint@tecmint ~/Linux-Tricks $ file EDWARD-MAYA-2011-2012-NEW-REMIX.mp3 
    EDWARD-MAYA-2011-2012-NEW-REMIX.mp3: Audio file with ID3 version 2.3.0, contains: MPEG ADTS, layer III, v1, 192 kbps, 44.1 kHz, JntStereo
    
    tecmint@tecmint ~/Linux-Tricks $ file /dev/sda1
    /dev/sda1: block special 
    
    tecmint@tecmint ~/Linux-Tricks $ file /dev/tty1
    /dev/tty1: character special 

#### 2. Determining the file type using ‘ls’ and ‘dir’ commands ####

Another way of determining the type of a file is by performing a long listing using the ls and [dir][4] commands.

Using ls -l to determine the type of a file.

When you view the file permissions, the first character shows the file type and the other charcters show the file permissions.

    tecmint@tecmint ~/Linux-Tricks $ ls -l
    total 6908
    drwxr-xr-x 2 tecmint tecmint    4096 Sep  9 11:46 BACKUP
    -rw-r--r-- 1 tecmint tecmint 1075620 Sep  9 11:47 crossroads-stable.tar.gz
    -rwxr----- 1 tecmint tecmint 5916085 Sep  9 11:49 EDWARD-MAYA-2011-2012-NEW-REMIX.mp3
    -rw-r--r-- 1 tecmint tecmint   42122 Sep  9 11:49 Linux-Security-Optimization-Book.gif
    -rw-r--r-- 1 tecmint tecmint   17627 Sep  9 11:46 master.zip
    -rw-r--r-- 1 tecmint tecmint       5 Sep  9 11:48 num.txt
    -rw-r--r-- 1 tecmint tecmint       0 Sep  9 11:46 reggea.xspf
    -rw-r--r-- 1 tecmint tecmint       5 Sep  9 11:47 tmp-link

Using ls -l to determine block and character files.

    tecmint@tecmint ~/Linux-Tricks $ ls -l /dev/sda1
    brw-rw---- 1 root disk 8, 1 Sep  9 10:53 /dev/sda1
    
    tecmint@tecmint ~/Linux-Tricks $ ls -l /dev/tty1
    crw-rw---- 1 root tty 4, 1 Sep  9 10:54 /dev/tty1

Using dir -l to determine the type of a file.

    tecmint@tecmint ~/Linux-Tricks $ dir -l
    total 6908
    drwxr-xr-x 2 tecmint tecmint    4096 Sep  9 11:46 BACKUP
    -rw-r--r-- 1 tecmint tecmint 1075620 Sep  9 11:47 crossroads-stable.tar.gz
    -rwxr----- 1 tecmint tecmint 5916085 Sep  9 11:49 EDWARD-MAYA-2011-2012-NEW-REMIX.mp3
    -rw-r--r-- 1 tecmint tecmint   42122 Sep  9 11:49 Linux-Security-Optimization-Book.gif
    -rw-r--r-- 1 tecmint tecmint   17627 Sep  9 11:46 master.zip
    -rw-r--r-- 1 tecmint tecmint       5 Sep  9 11:48 num.txt
    -rw-r--r-- 1 tecmint tecmint       0 Sep  9 11:46 reggea.xspf
    -rw-r--r-- 1 tecmint tecmint       5 Sep  9 11:47 tmp-link

#### 3. Counting number of files of a specific type ####

Next we shall look at tips on counting number of files of a specific type in a given directory using the ls, [grep][5] and [wc][6] commands. Communication between the commands is achieved through named piping.

- grep – command to search according to a given pattern or regular expression.
- wc – command to count lines, words and characters.

Counting number of regular files

In Linux, regular files are represented by the `–` symbol.

    tecmint@tecmint ~/Linux-Tricks $ ls -l | grep ^- | wc -l
    7

**Counting number of directories**

In Linux, directories are represented by the `d` symbol.

    tecmint@tecmint ~/Linux-Tricks $ ls -l | grep ^d | wc -l
    1

**Counting number of symbolic and hard links**

In Linux, symblic and hard links are represented by the l symbol.

    tecmint@tecmint ~/Linux-Tricks $ ls -l | grep ^l | wc -l
    0

**Counting number of block and character files**

In Linux, block and character files are represented by the `b` and `c` symbols respectively.

    tecmint@tecmint ~/Linux-Tricks $ ls -l /dev | grep ^b | wc -l
    37
    tecmint@tecmint ~/Linux-Tricks $ ls -l /dev | grep ^c | wc -l
    159

#### 4. Finding files on a Linux system ####

Next we shall look at some commands one can use to find files on a Linux system, these include the locate, find, whatis and which commands.

**Using the locate command to find files**

In the output below, I am trying to locate the [Samba server configuration][7] for my system.

    tecmint@tecmint ~/Linux-Tricks $ locate samba.conf
    /usr/lib/tmpfiles.d/samba.conf
    /var/lib/dpkg/info/samba.conffiles

**Using the find command to find files**

To learn how to use the find command in Linux, you can read our following article that shows more than 30+ practical examples and usage of find command in Linux.

- [35 Examples of ‘find’ Command in Linux][8]

**Using the whatis command to locate commands**

The whatis command is mostly used to locate commands and it is special because it gives information about a command, it also finds configurations files and manual entries for a command.

    tecmint@tecmint ~/Linux-Tricks $ whatis bash
    bash (1)             - GNU Bourne-Again SHell
    
    tecmint@tecmint ~/Linux-Tricks $ whatis find
    find (1)             - search for files in a directory hierarchy
    
    tecmint@tecmint ~/Linux-Tricks $ whatis ls
    ls (1)               - list directory contents

**Using which command to locate commands**

The which command is used to locate commands on the filesystem.

    tecmint@tecmint ~/Linux-Tricks $ which mkdir
    /bin/mkdir
    
    tecmint@tecmint ~/Linux-Tricks $ which bash
    /bin/bash
    
    tecmint@tecmint ~/Linux-Tricks $ which find
    /usr/bin/find
    
    tecmint@tecmint ~/Linux-Tricks $ $ which ls
    /bin/ls

#### 5. Working with time on your Linux system ####

When working in a networked environment, it is a good practice to keep the correct time on your Linux system. There are certain services on Linux systems that require correct time to work efficiently on a network.

We shall look at commands you can use to manage time on your machine. In Linux, time is managed in two ways: system time and hardware time.

The system time is managed by a system clock and the hardware time is managed by a hardware clock.

To view your system time, date and timezone, use the date command as follows.

    tecmint@tecmint ~/Linux-Tricks $ date
    Wed Sep  9 12:25:40 IST 2015

Set your system time using date -s or date –set=”STRING” as follows.

    tecmint@tecmint ~/Linux-Tricks $ sudo date -s "12:27:00"
    Wed Sep  9 12:27:00 IST 2015
    
    tecmint@tecmint ~/Linux-Tricks $ sudo date --set="12:27:00"
    Wed Sep  9 12:27:00 IST 2015

You can also set time and date as follows.

    tecmint@tecmint ~/Linux-Tricks $ sudo date 090912302015
    Wed Sep  9 12:30:00 IST 2015

Viewing current date from a calendar using cal command.

    tecmint@tecmint ~/Linux-Tricks $ cal
       September 2015     
    Su Mo Tu We Th Fr Sa  
           1  2  3  4  5  
     6  7  8  9 10 11 12  
    13 14 15 16 17 18 19  
    20 21 22 23 24 25 26  
    27 28 29 30      

View hardware clock time using the hwclock command.

    tecmint@tecmint ~/Linux-Tricks $ sudo hwclock
    Wednesday 09 September 2015 06:02:58 PM IST  -0.200081 seconds

To set the hardware clock time, use hwclock –set –date=”STRING” as follows.

    tecmint@tecmint ~/Linux-Tricks $ sudo hwclock --set --date="09/09/2015 12:33:00"
    
    tecmint@tecmint ~/Linux-Tricks $ sudo hwclock
    Wednesday 09 September 2015 12:33:11 PM IST  -0.891163 seconds

The system time is set by the hardware clock during booting and when the system is shutting down, the hardware time is reset to the system time.

Therefore when you view system time and hardware time, they are the same unless when you change the system time. Your hardware time may be incorrect when the CMOS battery is weak.

You can also set your system time using time from the hardware clock as follows.

    $ sudo hwclock --hctosys

It is also possible to set hardware clock time using the system clock time as follows.

    $ sudo hwclock --systohc

To view how long your Linux system has been running, use the uptime command.

    tecmint@tecmint ~/Linux-Tricks $ uptime
    12:36:27 up  1:43,  2 users,  load average: 1.39, 1.34, 1.45
    
    tecmint@tecmint ~/Linux-Tricks $ uptime -p
    up 1 hour, 43 minutes
    
    tecmint@tecmint ~/Linux-Tricks $ uptime -s
    2015-09-09 10:52:47

### Summary ###

Understanding file types is Linux is a good practice for begginers, and also managing time is critical especially on servers to manage services reliably and efficiently. Hope you find this guide helpful. If you have any additional information, do not forget to post a comment. Stay connected to Tecmint.

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via: http://www.tecmint.com/manage-file-types-and-set-system-time-in-linux/

作者：[Aaron Kili][a]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)

本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出

[a]:http://www.tecmint.com/author/aaronkili/
[1]:http://www.tecmint.com/tag/linux-tricks/
[2]:http://www.tecmint.com/free-online-linux-learning-guide-for-beginners/
[3]:http://www.tecmint.com/10-useful-linux-command-line-tricks-for-newbies/
[4]:http://www.tecmint.com/linux-dir-command-usage-with-examples/
[5]:http://www.tecmint.com/12-practical-examples-of-linux-grep-command/
[6]:http://www.tecmint.com/wc-command-examples/
[7]:http://www.tecmint.com/setup-samba-file-sharing-for-linux-windows-clients/
[8]:http://www.tecmint.com/35-practical-examples-of-linux-find-command/