Informatics1-2018/Lab04
A MathWikiből
(Változatok közti eltérés)
(Új oldal, tartalma: „= Linux permissions = * Permission groups ** '''s'''uper'''u'''ser (su), sys admins ** '''owner''', the user who made the file/directory, ex. <tt>someone</tt> ** '''gro…”) |
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| 1. sor: | 1. sor: | ||
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= Linux permissions = | = Linux permissions = | ||
* Permission groups | * Permission groups | ||
| 47. sor: | 49. sor: | ||
$ _ | $ _ | ||
</PRE> | </PRE> | ||
| − | + | The <tt>public_html</tt> folder is owned by <tt>borbely</tt>, its group is <tt>student</tt>, permissions: <tt>drwxr-xr-x</tt> | |
| − | * | + | * type: it is a '''d'''irectory |
| − | * | + | * my permissions '''rwx''' means that owner can do anything |
| − | * | + | * other students' permissions: '''r-x''', they can read but not write |
| − | * | + | * others: '''r-x''', they can still read but not write |
| − | + | Numerically, you can encode this in 3 digits. | |
| − | + | The three numbers are (from left to right): owner, group and others. The munbers 4: read, 2: write, 1: execute. | |
| − | + | They can be added. | |
| − | + | Example: <tt>/home/student/borbely/public_html</tt> has permission: <tt>755</tt> meaning | |
| − | * owner (<tt>borbely</tt>) <tt>7=4+2+1</tt>: | + | * owner (<tt>borbely</tt>) <tt>7=4+2+1</tt>: read, write, execute |
| − | * group (<tt>student</tt>) <tt>5=4+1</tt>: | + | * group (<tt>student</tt>) <tt>5=4+1</tt>: read and execute |
| − | * other <tt>5=4+1</tt>: | + | * other <tt>5=4+1</tt>: read and execute |
=== chmod === | === chmod === | ||
| − | + | You can change the permissions with <tt>chmod</tt> Examples: | |
| − | * <tt>chmod 700 ~/info_hazi</tt>: | + | * <tt>chmod 700 ~/info_hazi</tt>: nobody can see anything, except me (of course superusers still can see it). |
| − | * <tt>chmod 750 ~/important_work</tt>: | + | * <tt>chmod 750 ~/important_work</tt>: In this folder one can share data with group members, but not others. Also group can only see it, not modify. |
| − | * <tt>chmod 754 -R ~/public_html</tt>: | + | * <tt>chmod 754 -R ~/public_html</tt>: The '''-R''' applies the permissions recursively in the subfolders of the folder, and every file in it. |
| − | === | + | === More info === |
* <tt>man chmod</tt> | * <tt>man chmod</tt> | ||
| − | * [http://www.comptechdoc.org/os/linux/usersguide/linux_ugfilesp.html | + | * [http://www.comptechdoc.org/os/linux/usersguide/linux_ugfilesp.html] |
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A lap 2018. szeptember 24., 12:40-kori változata
Linux permissions
- Permission groups
- superuser (su), sys admins
- owner, the user who made the file/directory, ex. someone
- group, a subset of users with a distinct name, ex. student
- others, everyone else, public, guest, untrusted unsers
- Types of permissions
- w: Write, can modify
- r: Read, can read
- x: eXecute, run a program, or list a directory
- -: none
It is specified who can do what, ex:
- owner can write, read and execute
- its group can read and execute, but not modify
- others cannot do anything
The superusers (su) can do anything at any time, only a superuser can make an other user super.
These can be expressed with a set of three alpha-numeric charactes:
- u: user, owner
- g: group
- o: others
- a: all of the above
- read: r or 4
- write: w or 2
- execute: x or 1
- none: - or 0
The a is not the same as o, because it is possible that a group does not have a permission, but someone outside of the groups has.
The permissions can be represented with a 10 character string:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| type | owner | group | others | ||||||
| read | write | execute | read | write | execute | read | write | execute | |
$ ls -l ~ drwxr-xr-x 8 borbely student 4096 Aug 30 23:24 Desktop drwxr-xr-x 2 borbely student 4096 Mar 27 2012 Downloads drwxr-xr-x 2 borbely student 4096 Oct 20 2009 Drives drwx------ 2 borbely student 4096 Apr 20 10:42 mail drwxr-xr-x 7 borbely student 4096 Sep 6 13:01 public_html $ _
The public_html folder is owned by borbely, its group is student, permissions: drwxr-xr-x
- type: it is a directory
- my permissions rwx means that owner can do anything
- other students' permissions: r-x, they can read but not write
- others: r-x, they can still read but not write
Numerically, you can encode this in 3 digits. The three numbers are (from left to right): owner, group and others. The munbers 4: read, 2: write, 1: execute. They can be added. Example: /home/student/borbely/public_html has permission: 755 meaning
- owner (borbely) 7=4+2+1: read, write, execute
- group (student) 5=4+1: read and execute
- other 5=4+1: read and execute
chmod
You can change the permissions with chmod Examples:
- chmod 700 ~/info_hazi: nobody can see anything, except me (of course superusers still can see it).
- chmod 750 ~/important_work: In this folder one can share data with group members, but not others. Also group can only see it, not modify.
- chmod 754 -R ~/public_html: The -R applies the permissions recursively in the subfolders of the folder, and every file in it.
More info
- man chmod
- [1]
