Filesystem#
In this page considered tools that are used for system management in linux.
Files and directories#
There are tools that allow to manipulate with files and folders using Linux command system.
Utility |
Description |
|---|---|
|
List files and directories. |
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Change directory. |
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Create directories. |
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Remove empty directories. |
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Remove files and directories. |
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Move or rename files and directories. |
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Copy files and directories. |
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Create empty files or update timestamps. |
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Search for files and directories. |
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Quickly find files by name (uses a prebuilt database). |
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Display directories as a tree structure. |
Check details on the specific page.
Disk usage (du)#
The du command is used to check disk usage by different paths in the filesystem. It provides information about how much space is being used by files and directories.
The following cell creates several folders and files. Notably, linux/du_example/megabytes_file is created with a size of exactly 2.5 megabytes, whereas linux/du_example/folder/small_file contains only a single short line, making it an extremely small file.
mkdir linux/du_example
mkdir linux/du_example/folder
dd if=/dev/zero of=linux/du_example/megabutes_file bs=1M count=2 &> /dev/null
dd if=/dev/zero of=linux/du_example/megabutes_file bs=512K count=1 oflag=append conv=notrunc &>/dev/null
echo "this is short message" >> linux/du_example/folder/small_file
Now let’s try the du command. The following options are also added:
a: prints both files and folders.h: displays file sizes in a human-readable format.
These options are really useful in my opinion.
du -ah linux/du_example/
2,5M linux/du_example/megabutes_file
4,0K linux/du_example/folder/small_file
8,0K linux/du_example/folder
2,6M linux/du_example/
After all don’t forget foder that was used for experiments.
rm -r linux/du_example
Archiving#
This section discusses utilities in Linux related to archiving: combining a set of files into a single compact file and extracting it back to the original files. Below is a list of popular archive utilities:
Utility |
Description |
|---|---|
|
A widely-used tool for creating, extracting, and managing tarball archives (e.g., |
|
Compresses files using the GNU zip algorithm, typically creating |
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Compresses files using the Burrows-Wheeler algorithm, typically creating |
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Compresses files with high compression efficiency, typically creating |
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Creates compressed archives in |
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Extracts |
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A high-compression utility for |
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Creates, modifies, and extracts archives, often used for |
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Creates RAR archives, known for good compression ratios; proprietary software. |
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Extracts RAR files. |
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Compresses files using LZMA (Lempel-Ziv-Markov chain algorithm), predecessor to |
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Combines tar archiving and LZMA compression, resulting in |
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Combines tar archiving and XZ compression, resulting in |
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Compresses files with high speed and efficiency, creating |
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Archives files for use with tape backups or streams. |
Find out more in the particular page.
Consider the example of an archive file generated in the following cell.
for ((i=0; i<1000000; i++))
do
echo -n "a" >> /tmp/archive_me
done
du -h /tmp/archive_me
980K /tmp/archive_me
File just contains repeated a, it is repeated so many times that all files take 980K.
The next cell applies archiving to the created file.
tar -cJvf /tmp/archive.tar.xz /tmp/archive_me
du -h /tmp/archive.tar.xz
tar: Removing leading `/' from member names
/tmp/archive_me
4,0K /tmp/archive.tar.xz
Result takes only 4KB.
The following cell restores the original file.
mkdir /tmp/unarchived
tar -xJvf /tmp/archive.tar.xz -C /tmp/unarchived
tmp/archive_me
This is the file tree we got after unarchiving.
tree /tmp/unarchived
/tmp/unarchived
└── tmp
└── archive_me
1 directory, 1 file
Finally, check that the contents of the file have been restored correctly.
head -c 100 /tmp/unarchived/tmp/archive_me
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Permission/ownership#
Each file in Linux contains special attributes that specify permissions and ownership for that file. Permissions determine the ability of a user or group to read, write, or execute a file.
There are central commands to handle permissions and ownership:
ls -l: Shows the content of a folder, along with information about the owner and permissions for each item.chown: Allows you to change the owner of a file or folder.chmod: Allows you to change the permissions of a file.
The following cell creates a file and shows its initial attributes:
[ -d /tmp/permissions ] && rm -r /tmp/permissions
mkdir /tmp/permissions
cd /tmp/permissions
touch toy_file
ls -l
total 0
-rw-r--r-- 1 root root 0 Feb 2 18:14 toy_file
Here, -rw-r--r-- corresponds to the permissions, and root root describes the user and group, respectively.
The following cell creates a new user and grants them permissions for that file using the chown command.
useradd perm_exam
chown -c perm_exam toy_file
ls -l
userdel perm_exam
changed ownership of 'toy_file' from root to perm_exam
total 0
-rw-r--r-- 1 perm_exam root 0 Feb 2 18:08 toy_file
As a result, in the output of ls -l, perm_exam is listed in the user field.
Finally, the last cell changes the permission attributes of the file using the chmod command.
chmod 417 toy_file
ls -l
total 0
-r----xrwx 1 1001 root 0 Feb 2 18:08 toy_file
It changes the first field corresponding to the toy_file - so the permissions are now different.
test#
test is a core linux utility that allows you to build expressions that depend on files. For more details see the corresponding page in the GNU manual.
Note: for this command there is a very popular alias [ <parameters> ] .
Consider the basic example of using test. The following cell tries to check if the file /tmp/wow exists.
test -f /tmp/wow
echo $?
1
Since it wasn’t created, we got the typical error result output - 1.
The following cell repeates previous experiment but now, it creates file before running test -f /tmp/wow.
echo "info" > /tmp/wow
test -f /tmp/wow
echo $?
rm /tmp/wow
0
So the result code is 0, that means that file we checked truly exists.
Negation#
You can negotiate the test by using ! in the list of parameters.
For example, ! -f will return true if there is no file in the given path. The following cell just shows how it works for a file that doesn’t exist - there’s nothing in the result, which means the cell exits with a 0 status code.
test ! -f /tmp/wow
This cell creates a file before executing test ! as the result there is a 1 status code.
echo "info" > /tmp/wow
test ! -f /tmp/wow
echo $?
rm /tmp/wow
1
Symbolic links#
Symbolic link is a file that points to the other file or directory, in fact, it is just another name for some file. You can manipulate with symbolic links with the ln command.
As an example, consider the process of creating a symbolik link. The following cell creates an experimental folder and file to which symbolic link will point.
mkdir /tmp/symb_links
cd /tmp/symb_links
cat << EOF > original_file
hello from
original file
EOF
You can create the link with ln -s <target> <link name>.
ln -s original_file symb_link
Make sure that the link was really created by displaying the result of the ls in long format.
ls -l
total 4
-rw-rw-r-- 1 fedor fedor 34 Mar 30 12:20 original_file
lrwxrwxrwx 1 fedor fedor 13 Mar 30 12:19 symb_link -> original_file
As a result the created symb_link file have a special color and it points (->) to the original file.
The following cell shows the contents of the symb_link file.
cat symb_link
hello from
original file
It corresponds to the contents of the original_file.
But this applies to any kind of manipulation—the following cell adds a “new line” to symb_link, and as a result, that line appears in original_file.
echo "new line" >> symb_link
cat original_file
hello from
original file
new line