Commands Tour
ls
The ls command is used to list the contents of a directory. It is probably the most commonly used Linux command. It can be used in a number of different ways. Here are some examples:
| Command | Result |
|---|---|
| ls | List the files in the working directory |
| ls /bin | List the files in the /bin directory (or any other directory you care to specify) |
| ls -l | List the files in the working directory in long format |
| ls -l /etc /bin | List the files in the /bin directory and the /etc directory in long format |
| ls -la .. | List all files (even ones with names beginning with a period character, which are normally hidden) in the parent of the working directory in long format |
These examples also point out an important concept about commands. Most commands operate like this:
command -options arguments
where command is the name of the command, -options is one or more adjustments to the command's behavior, and arguments is one or more "things" upon which the command operates.
In the case of ls, we see that ls is the name of the command, and that it can have one or more options, such as -a and -l, and it can operate on one or more files or directories.
A Closer Look At Long Format
If you use the -l option with ls, you will get a file listing that contains a wealth of information about the files
-rw------- 1 bshotts bshotts 576 Apr 17 1998 weather.txt
drwxr-xr-x 6 bshotts bshotts 1024 Oct 9 1999 web_page
-rw-rw-r-- 1 bshotts bshotts 276480 Feb 11 20:41 web_site.tar
-rw------- 1 bshotts bshotts 5743 Dec 16 1998 xmas_file.txt
---------- ------- ------- -------- ------------ -------------
| | | | | |
| | | | | File Name
| | | | |
| | | | +--- Modification Time
| | | |
| | | +------------- Size (in bytes)
| | |
| | +----------------------- Group
| |
| +-------------------------------- Owner
|
+---------------------------------------------- File Permissions
- File Name
- The name of the file or directory.
- Modification Time
- The last time the file was modified. If the last modification occurred more than six months in the past, the date and year are displayed. Otherwise, the time of day is shown.
- Size
- The size of the file in bytes.
- Group
- The name of the group that has file permissions in addition to the file's owner.
- Owner
- The name of the user who owns the file.
- File Permissions
- A representation of the file's access permissions. The first character is the type of file. A "-" indicates a regular (ordinary) file. A "d" indicates a directory. The second set of three characters represent the read, write, and execution rights of the file's owner. The next three represent the rights of the file's group, and the final three represent the rights granted to everybody else.
- cd into each directory.
- Use ls to list the contents of the directory.
- If you see an interesting file, use the file command to determine its contents.
- For text files, use less to view them.
Interesting directories and their contents Directory Description / The root directory where the file system begins. In most cases the root directory only contains subdirectories. /boot This is where the Linux kernel and boot loader files are kept. The kernel is a file called vmlinuz. /etc The /etc directory contains the configuration files for the system. All of the files in /etc should be text files. Points of interest: - /etc/passwd
- The passwd file contains the essential information for each user. It is here that users are defined.
- /etc/fstab
- The fstab file contains a table of devices that get mounted when your system boots. This file defines your disk drives.
- /etc/hosts
- This file lists the network host names and IP addresses that are intrinsically known to the system.
- /etc/init.d
- This directory contains the scripts that start various system services typically at boot time.
/bin, /usr/bin These two directories contain most of the programs for the system. The /bin directory has the essential programs that the system requires to operate, while /usr/bin contains applications for the system's users. /sbin, /usr/sbin The sbin directories contain programs for system administration, mostly for use by the superuser. /usr The /usr directory contains a variety of things that support user applications. Some highlights: - /usr/share/X11
- Support files for the X Windows system
- /usr/share/dict
- Dictionaries for the spelling checker. Bet you didn't know that Linux had a spelling checker. Seelook and ispell.
- /usr/share/doc
- Various documentation files in a variety of formats.
- /usr/share/man
- The man pages are kept here.
- /usr/src
- Source code files. If you installed the kernel source code package, you will find the entire Linux kernel source code here.
/usr/local /usr/local and its subdirectories are used for the installation of software and other files for use on the local machine. What this really means is that software that is not part of the official distribution (which usually goes in /usr/bin) goes here.
When you find interesting programs to install on your system, they should be installed in one of the/usr/local directories. Most often, the directory of choice is /usr/local/bin./var The /var directory contains files that change as the system is running. This includes: - /var/log
- Directory that contains log files. These are updated as the system runs. You should view the files in this directory from time to time, to monitor the health of your system.
- /var/spool
- This directory is used to hold files that are queued for some process, such as mail messages and print jobs. When a user's mail first arrives on the local system (assuming you have local mail), the messages are first stored in /var/spool/mail
/lib The shared libraries (similar to DLLs in that other operating system) are kept here. /home /home is where users keep their personal work. In general, this is the only place users are allowed to write files. This keeps things nice and clean /root This is the superuser's home directory. /tmp /tmp is a directory in which programs can write their temporary files. /dev The /dev directory is a special directory, since it does not really contain files in the usual sense. Rather, it contains devices that are available to the system. In Linux (like Unix), devices are treated like files. You can read and write devices as though they were files. For example /dev/fd0 is the first floppy disk drive, /dev/sda (/dev/hda on older systems) is the first IDE hard drive. All the devices that the kernel understands are represented here. /proc The /proc directory is also special. This directory does not contain files. In fact, this directory does not really exist at all. It is entirely virtual. The /proc directory contains little peep holes into the kernel itself. There are a group of numbered entries in this directory that correspond to all the processes running on the system. In addition, there are a number of named entries that permit access to the current configuration of the system. Many of these entries can be viewed. Try viewing/proc/cpuinfo. This entry will tell you what the kernel thinks of your CPU. /media,/mnt Finally, we come to /media, a normal directory which is used in a special way. The /media directory is used for mount points. This process of attaching a device to the tree is called mounting. For a device to be available, it must first be mounted.
When your system boots, it reads a list of mounting instructions in the file /etc/fstab, which describes which device is mounted at which mount point in the directory tree. This takes care of the hard drives, but you may also have devices that are considered temporary, such as CD-ROMs and floppy disks. Since these are removable, they do not stay mounted all the time. The /media directory is used by the automatic device mounting mechanisms found in modern desktop oriented Linux distributions. On systems that require manual mounting of removable devices, the /mnt directory provides a convenient place for mounting these temporary devices. You will often see the directories /mnt/floppy and /mnt/cdrom. To see what devices and mount points are used, type mount.
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