Lab No. 2: The File System and Working with Files¶
After completing this lab, students will be able to:
- Inspect and navigate the linux filesystem
- Create, remove and alter files and directories
The File System¶
A file system is a method for organizing and storing data. Without a file sytem, the operating sytem (and the users) would have a hard time locating files that are needed to perform tasks. The file system consists of files and their attributes and relationships between files.
The Linux file system is composed of files and directories.
A file is a collection of data that is logically related, and it is the smallest unit of storage in the Unix file system.
Directories are also file, but they are special since they may contain other files and other directories (a physical analogy isa folder or envelope where you can use to organize and store papers, or other envelopes).
In this way, the files sytem is organized in a hierarchical structure that resembles a tree, typically represented upside down (in the same fashion as a family tree).
The top directory in a Linux file system is called the root directory, or simply, the root, and it is represented by the / (slash) character.
The standard hierarchy of Linux Filesystems is published by the Linux Foundation as a specification (available under https://refspecs.linuxfoundation.org/fhs.shtml). The following directories are required by the standard (Refer to Table 3-4 in TLCL for more details)
| Directory | Description |
| / | root directory |
| /bin | Essential command that must be present for boot/recovery |
| /boot | Contains the boot loader and kernel files |
| /dev | Device files. |
| /etc | System configuration |
| /home | Users directories and files |
| /lib | Essential shared libraries and kernel modules |
| /media | Mount point for removable media (USB Drives, CD-ROMS) |
| /mnt | Mount point for mounting a filesystem manually |
| /opt | Add-on application software packages (“optional”) |
| /proc | Process information pseudo-file system (contains runtime information). |
| /root | Home directory for the “root” user. |
| /run | Data required by running processes |
| /sbin | System binaries. |
| /tmp | Temporary files |
| /usr | All the programs and support files to be used by regular users |
| /var | Variable data (logs, user mail, spool files, etc). |
Creating directories and files¶
The mkdir utility creates new directories. It requires as arguments the pathnames of the directories to be created. The following example shows the commands required to generate the directory structure shown below (the shown output assumes that your home directory is empty. If that is not the case, then existing files will show in the output of the ls command.)
[user@blue ~]$ ls [user@blue ~]$ mkdir vehicles [user@blue ~]$ ls vehicles [user@blue ~]$ mkdir -p vehicles/cars/sedan [user@blue ~]$ ls vehicles/cars sedan [user@blue ~]$ mkdir -p vehicles/cars/pickup vehicles/cars/suv [user@blue ~]$ ls vehicles/cars pickup sedan suv
Notice that we did not create the cars directory directly, and instead we used the -p option to instruct the mkdir command to make any non-existing intermeditate directories.
Note also that you can create more than one directory at a time.
The tree command is useful to have a directory listing in a tree like structure:
[user@blue ~]$ tree vehicles
vehicles
└── cars
├── pickup
├── sedan
└── suv
4 directories, 0 files
To remove directories you can use the rmdir command.
Just as mkdir, it requires the pathnames of the directories to be removed.
However, rmdir has the limitation that it only works with empty directories.
To remove directories that are not empty, you can use the rm -r command.
Let’s remove the ./vehicles/cars/suv directory:
[user@blue ~]$ rmdir vehicles/cars/suv
[user@blue ~]$ rm -r vehicles/cars/pickup
[user@blue ~]$ tree vehicles
vehicles
└── cars
└── sedan
2 directories, 0 files
Moving files¶
The mv command can be used for two purposes: rename a file/directory, or move the file/directory to another path.
Let’s rename the sedan directory to coupe:
[user@blue ~]$ mv vehicles/cars/sedan vehicles/cars/coupe
[user@blue ~]$ tree vehicles
vehicles
└── cars
└── coupe
2 directories, 0 files
Noticed that the first argument is the source file or directory and the second is the destination directory or file. In this case, since the destination did not exist, then it perfoms a “rename”
To see how the mv command can be used to move files, let’s recreate the sedan directory and and empty file under it:
[user@blue ~]$ mkdir vehicles/cars/sedan
[user@blue ~]$ touch vehicles/cars/sedan/shelby
[user@blue ~]$ tree vehicles
vehicles
└── cars
├── coupe
└── sedan
└── shelby
3 directories, 1 file
Let’s move shelby from the sedan directory to the coupe directory (where it belongs, obviously).
[user@blue ~]$ mv vehicles/cars/sedan/shelby vehicles/cars/coupe
[user@blue ~]$ tree vehicles
vehicles/
└── cars
├── coupe
│ └── shelby
└── sedan
3 directories, 1 file
Notice that in this case, the destination exists, and it is a directory, so the result of the command is that the file is move to the destination directory.
Copying files¶
The cp command is used to copy files or directories. In the following example, a file is created by redirecting the output of the echo command into a file called original.
The cat command reads that file and prints that on the screen, this is done as a verification step.
original is then copied into a file called clone. Notice how the contents of clone are the same as the contents of original.
[user@blue ~]$ echo "This text is the content" > original [user@blue ~]$ ls original vehicles [user@blue ~]$ cat original This text is the content [user@blue ~]$ cp original clone [user@blue ~]$ ls clone original vehicles [user@blue ~]$ cat clone This text is the content
In order to copy directories, you need to provide the -r option to the cp command. This option stands for recursive, and basically it means that it will traverse the whole tree under the directory that you want to copy.
Lab Report
- There is a directory named
mailinside the/var/logdirectory. What is the relative path to that directory if you are in your home directory? - Absolute and relative pathnames can be mixed. Consider the following path:
/usr/include/curl/./././///../boost/random/../math. Simplify that path so it does not use relative references (hint: try it with thecdcommand).
The following diagram corresponds to a portion of the filesystem in blue. Fill out the empty elements in A, B, C and D.
- A
- B
- C
- D
- What is the oldest file in the
/usr/bindirectory? - What is the newest kernel file in blue (kernel files are named with the suffix
vmlinuz)? - We want to make a backup of the
vehiclesdirectory into a directory calledvehicles_backup. What command will serve this purpose? - Provide a series of commands to create the following directory structure in your current working directory?
transport
├── bicycles
│ └── mountain
├── cars
│ ├── pickup
│ ├── sedan
│ │ └── compact
│ └── suv
└── jet
├── cargo
└── fighter
- Make your home the working directory. Run the following command: tar -xf /tmp/vehicles.tar. This will create three files with names of transportation vehicles in your working directory. Provide a list of commands that will result in moving the files to the corresponding directory within the
transportdirectory (durango is an SUV, prius a compact sedan, and stumpjumper is a mountain bike). - The three files should contain the Wikipedia link that corresponds to the name of the file. However, the file named
priusis incorrect. Provide a single command that will make the file name reflect the content of the file (e.g. the file name should befseriesinstead ofprius) and will place the file under the correct directory (~/transport/cars/pickup)