Basic concepts of linux
Day 3
Hello everyone welcome back !!!
Myself Swanik Santosh Gudekar and I am back with my blog. This is the third blog of Linux series. Today I attended the third session conducted by Master Pranav Jambare. It was a fun and exciting session.
Points Covered in This Session :
Hardlink
Softlink
Permission
Special Permission
HardLink :
HardLink is also a type of file that points to the same data as another file.
HardLink creates a separate copy of a file's data.
This means if the main file is renamed, relocated, or removed from the system it does not bother the copy created by HardLink it still works smoothly.
HardLinks cannot be created for directories, if does then it may cause circular reference or loop, which causes issues with file system operations and can lead to data corruption.
SYNTAX : ln [main_file][link_file]
SoftLink :
It is a type of file that points to another file or directory is said to be SoftLink in Linux.
It is also called a Symbolic Link.
When we open a SoftLink it redirects us to the original or main file or directory.
It is similar to the shortcuts in Windows.
SoftLink makes it easier to access files that are stored in different directories.
They do not take more additional space on your hard disk.
Softlink is a powerful tool that can be used to simplify file management in Linux.
SoftLink can't work or be accessed If the original file is removed or Deleted.
SYNTAX : ln -s [main_file][link_file]
Permission :
Linux is a multi-user operating system, so it has security to prevent people from accessing each other’s confidential files.
Permission is the set of access rights that determine what actions can be performed on a file or directory.
The permissions are primarily associated with three entites : Owner of the file, the group to which they belong, and others.
Eg. -rwxrwxrwx
| Letters | Definition |
| r | read the content of the files |
| w | write or modify the content of the files |
| x | execute the file |
Calculate the permission :
Read - 2^2 = 4
Write - 2^1 = 2
Execute - 2^0 = 1
Eg. A file might have read, write, and execute permission for owner and read, write permission for group and only read permission for other user.
Owner : rwx = 4+2+1 = 7
Group : rw- = 4+2+0 = 6
Other : r-- = 4+0+0 = 4
Hence the permission is 764.
Root User Permission :
| File | Directories | |
| Max | 666 | 777 |
| Default | 644 | 755 |
Normal User permission :
| File | Directories | |
| Max | 666 | 777 |
| Default | 664 | 775 |
Umask :
Umask stands for user file creation mask
The umask command specifies the permissions that the user does not want to be given out to the newly created file or directory.
We can provide the default permission to the file or directory using the command.
the umask command is used to set the default permission file permission for the newly created file and directory.
SYNTAX : umask <umasknumber>
eg. umask 766
Special Permission :
Linux uses some special permissions to allow certain capabilities that go beyond the basic rwx.
Special permissions allow for additional privileges over the standard permission sets.
Special permissions make up a fourth access level in addition to user, group, and other.
1) Sticky Bit :
Skicky bit works in directories.
This permission does not affect individual files.
However, at the directory level, it restricts file deletion.
Only the file owner, directory owner, and root user can delete or rename its files when a sticky bit is set to the directory.
To avoid such scenarios sticky bit is applied to the directory where you can create the files, and check someone else's file but can't rename and delete it.
SYNTAX :
To enable - chmod +t <dir name>
To disable - chmod -t <dir name>
2)SGID :
SGID stands for Set Group Identification.
If set on a file, it allows the file to be executed as the group that owns the file (similar to SUID).
If set on a directory, any files created in the directory will have their group ownership set to that of the directory owner.
SYNTAX :
To enable - chmod g+s <dir name>
To disable - chmod g-s<dir name>
3) SUID :
SUID stands for set Set Owner User Id.
A file with SUID always executes as the user who owns the file, regardless of the user passing the command.
When the SUID bit on an executable file is set, it signifies that the file will be executed with the same permissions as the executable's owner.
SYNTAX :
To enable : chmod u+s <dir name>
To disable : chmod u-s <dir name>
These were the topics covered by Master Pranav Jambare in the third session of Linux.
