Linux Commands for Beginners 21 - Changing Permissions Numerically — Transcript

Full transcript

1. 0:00[Music]
2. 0:21hello again everyone in today's video we
3. 0:24are going to revisit permissions we've
4. 0:26already gone over permissions in video
5. 0:28number 9 so if you haven't already seen
6. 0:30video 9 I highly suggest that you watch
7. 0:33that one first because in this video I'm
8. 0:36going to show you how to understand the
9. 0:38numerical value of permissions and in
10. 0:42video number 9 we took a introduction
11. 0:44look at permission so we're going to get
12. 0:46a little bit more advanced in this video
13. 0:49it's not too bad though so in this video
14. 0:51you'll understand the numerical value of
15. 0:53permissions and that's definitely an
16. 0:55important thing to know so let's go
17. 0:57ahead and dive right in so here are my
18. 0:59terminal I have a brand new Ubuntu
19. 1:03instance I created on Linode because I
20. 1:05wanted a clean instance for the purposes
21. 1:08of this video I didn't want to change
22. 1:10permissions on my actual files and
23. 1:12folders but it doesn't really matter
24. 1:14what you're using here because this is
25. 1:16pretty much the same across all Linux
26. 1:18distributions and what I did was I
27. 1:21created a folder and a text file called
28. 1:25documents and text file respectively so
29. 1:29what I'm going to do is again show you
30. 1:31how to understand the numerical value of
31. 1:34permissions but as a quick refresher
32. 1:37when you see the permission string which
33. 1:40is here on the Left which is what you
34. 1:42get when you use LS dash L the first
35. 1:45character here is either a D or a hyphen
36. 1:47and yes there could either be there
37. 1:49could be other things here but we're not
38. 1:50going to get into that primarily it's
39. 1:52going to be D for directory or a hyphen
40. 1:55for file and then from there we have
41. 1:56three groups of three so this is Group
42. 1:58one this is group two and this is Group
43. 2:02three and individual bits mean read
44. 2:04write and execute accordingly and a bit
45. 2:08can either be on or off so this AR if
46. 2:10it's odd will be the R so we see that it
47. 2:12is on if it was off the R would become -
48. 2:16the same for the other characters you
49. 2:17can't have a W here or X here it's read
50. 2:21write execute read write execute read
51. 2:24write execute that's all it can be it's
52. 2:26either it's on or it's off again watch
53. 2:29video 9 if that confuses you because you
54. 2:32should have already gone through that
55. 2:34in which case that would probably make
56. 2:36sense so each of these bits actually
57. 2:38have a numerical value so for example we
58. 2:41have R which again stands for read that
59. 2:44has a numerical value of 4w which stands
60. 2:47for right has a numerical value of 2x
61. 2:52which is short for execute has a
62. 2:55numerical value of 1 so 4 to 1
63. 2:59corresponds to read write and execute
64. 3:01just as you see here so that might look
65. 3:04kind of confusing but how does that look
66. 3:06in practice I think by seeing it in
67. 3:08practice you'll understand it a bit
68. 3:11better so here's what we're going to do
69. 3:13we're going to use the chmod command
70. 3:16which again we went over in video 9 but
71. 3:18basically that command is going to allow
72. 3:20us to change permissions and what I'm
73. 3:22going to do is change the permissions of
74. 3:24text file so what I'm going to do now is
75. 3:27do 4 0 0 and then what I want to change
76. 3:31permissions on again is text file what
77. 3:34do you think is going to happen let's go
78. 3:36ahead and find out so chmod 400 txt file
79. 3:42we have read Because read is worth 4 as
80. 3:47I mentioned earlier and 0 0 as you can
81. 3:51see means pretty much nothing so for
82. 3:54each of the last groups of 3 so Group 1
83. 3:58group 2 and group 3 which is user group
84. 4:05and other respectively
85. 4:07these actually correspond to that same
86. 4:10group of 3 as well so for here that I
87. 4:14change the two is user this 0 is group
88. 4:18and this 0 is other so each of these
89. 4:22numbers corresponds to one of the last
90. 4:24three groups in the permission string so
91. 4:27by giving it a value of 400 we're
92. 4:30basically saying that the user section
93. 4:33which is actually right here is worth a
94. 4:37value of 4 the other two sections here
95. 4:41and here are both worth 0 so for
96. 4:47example if I was to do four for four
97. 4:52that means everybody has read if I was
98. 4:57to do let's say zero for zero we can see
99. 5:04that group has read but no other section
100. 5:08has that so that's kind of weird you
101. 5:09probably won't see that in the real
102. 5:12world but you know you can do it much
103. 5:14the same way that I could simply do zero
104. 5:17zero four which gives other read access
105. 5:22but not the owner of the group again a
106. 5:24weird permission but that's just to show
107. 5:26you how that corresponds because every
108. 5:29time I move the value of four over the
109. 5:33read value also gets moved over as you
110. 5:35see so similarly if I was to change it
111. 5:39to 200 we can see that the owning user
112. 5:46has write permission and then if I
113. 5:48change that to zero to zero you see
114. 5:54right moved over to the next section and
115. 5:58then again that moved right over to the
116. 6:04last section
117. 6:05as I mentioned two is a numerical value
118. 6:09for right so how do you give each field
119. 6:13more than just one thing well it's
120. 6:16simple so we could do chmod 700 text
121. 6:22file let's see what that does
122. 6:27that gave user read write and execute
123. 6:30users the first field here corresponds
124. 6:34to the second field or the first field
125. 6:37in the set of three the first field of
126. 6:39course designates directory or file
127. 6:41seven is what you get when you add for
128. 6:44two and one the three values you could
129. 6:46possibly have so if you were to give it
130. 6:49for example six that gives it just read
131. 6:54and write that's because the execute bit
132. 6:56is worth one we took that away read is
133. 6:59worth four we
134. 7:01right is worth 2 4 plus 2 is 6 that's
135. 7:05how we got that we could do the same
136. 7:07thing and do let's just say 6 5 5 let's
137. 7:15see what that gives us so that's kind of
138. 7:18interesting it gives user read and write
139. 7:20group read and execute and other read
140. 7:24and execute no that's kind of kind of
141. 7:26weird we probably wouldn't want that but
142. 7:28what we could do 644 which is probably
143. 7:32something you're more likely to see in
144. 7:34the real world gives the owner read and
145. 7:38write the group read and other read as
146. 7:42well that basically means everybody can
147. 7:45read this file but only the owning user
148. 7:47can make changes to it or write to it
149. 7:50because we gave the owner 6 which is
150. 7:54basically for read and write to added
151. 7:58together then we gave group and other 4
152. 8:01which is read to come up with this
153. 8:05permission string right here now I
154. 8:07mentioned in video number 9 that execute
155. 8:10in a directory means something different
156. 8:12than file if it's a file with the
157. 8:14execute bit that means you can run it as
158. 8:15a program we can see here that the
159. 8:18folder has execute bit here that's
160. 8:21required to actually change directory
161. 8:23into that directory but we can modify
162. 8:26the permissions of the documents
163. 8:28directory the same way so chmod 755
164. 8:32against the documents directory and
165. 8:37again the command we entered was this
166. 8:39one this basically means that everybody
167. 8:42can read the contents of the directory
168. 8:44and go inside the directory but only the
169. 8:48owner is able to change the contents of
170. 8:51that directory
171. 8:52the owner has write permission if we
172. 8:55wanted everybody in the world to have
173. 8:56access full access 777 basically
174. 9:01highlights it in green that's not always
175. 9:02going to happen that's just a shell
176. 9:04customization but you can see that that
177. 9:06filled in every single permission bit we
178. 9:08could do the same thing to the text file
179. 9:14if we can see the text file has all the
180. 9:18bits set as well so seven gives it
181. 9:20everything for that field so now we have
182. 9:23a folder and a file that has everything
183. 9:27turned on and to take it away we could
184. 9:29simply do this which basically took that
185. 9:36away from other you do the same thing to
186. 9:39documents and the same thing happened to
187. 9:44documents so again read equals four
188. 9:48write equals to execute equals one you
189. 9:53can add these up any way you'd like put
190. 9:56the value where you'd like to change the
191. 9:59appropriate permission for and that'll
192. 10:01give you the numerical value of that
193. 10:03permission which might be useful to you
194. 10:06if you prefer that method or if that
195. 10:08works better for your use case now you
196. 10:11should actually be able to change
197. 10:12permission via number as well so I know
198. 10:15that was a relatively simple video guys
199. 10:17but in the original video when we went
200. 10:19over permissions that one was already
201. 10:21going on kind of long and I wanted to go
202. 10:24ahead and revisit this in another video
203. 10:26which I finally had a chance to do in
204. 10:29this one so I hope that was helpful for
205. 10:31you guys I'm gonna be creating some new
206. 10:33tutorials in this series I'll be editing
207. 10:36some coming up here pretty soon should
208. 10:37have them uploaded very soon so stay
209. 10:40tuned and there's going to be definitely
210. 10:42some more videos in the series thanks
211. 10:46for checking out my video I really
212. 10:47appreciate it if you found it useful
213. 10:49click that like button and if you
214. 10:51haven't already done so make sure you
215. 10:53subscribe so you'll see the latest
216. 10:55content as soon as it becomes available
217. 10:57if you want to help me out there's links
218. 10:59down below for my patreon page as well
219. 11:02as links for purchasing my Linux books
220. 11:05and also my affiliate store which has a
221. 11:08listing of Linux compatible hardware
222. 11:09that I've actually tested personally
223. 11:12thanks again for watching and I'll see
224. 11:14you in the next video