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Hello everyone.

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In this lesson I'm going to talk about U-mask.

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First, let's understand what is U-mask?

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U-mask is the default permission values for files and directories is four digits numbers.

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For example, the default value of u-mask in Linux operating system is 0022.

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The first digit as we can see here, the zero.

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We ignore this digits for now.

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We will talk about it in a different lesson.

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It's use for a special permissions.

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For example, the set user ID or set group ID or a sticky bit.

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The second digit, it's permission set for the user, the third one or the third digit to hear it's

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permission set for group.

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The fourth digit to hear is permission set for other.

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If you would like to display or show what is the default mask of the system, we will run the command

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you mask if we would like to show it in a symbolic sign or a symbolic way.

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So we run the mask and option here.

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Dash uppercase s.

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If you would like to change and set the default UMass 20026 we run the command you mask zero 0 to 6.

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So here, if we would like to know what is the default mask for the root user and for the origin user.

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So there are different here, as you can see here between the root user and the default user.

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So for the root, the default mask value here is 0022 for the other user is 0002.

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Now let's move on to the next slide.

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So as we can see here, I came up with this equation.

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So make it easier for you to understand how we can get the default permission either for the directories

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or the files.

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Let's start with directories.

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So if you would like to get the default permissions so we'll get the value here seven, seven, seven

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minus the U-mask, then you will get the default permission for the files if you'd like to get the default

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permission.

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So it will be six, six, six minus the mask.

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So the next table, as we can see here, it shows how to calculate the default permission from the U-mask.

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So as I said, we have the root and we have the origin user.

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So the default mask for the root is 0022 and for the other user is 0002.

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Now let's get the default directory permissions and the file permission.

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Let's start with the directory here first here in this section.

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So for the root, we'll get this number, the default and minus seven, seven, seven and we get the

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number here is 755 for the ordinary user.

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We'll get this digits here.

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Seven, seven, seven -0 zero two and we'll get the value here, seven, seven, five.

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Now let's move on to this section here to the default value permission.

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And I start with the root first.

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So here will be six, six, six -0 two two, which is this one, the default mask and we'll get the

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default file permission six, four, four.

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Now let's do it for the origin user.

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We'll get the 000 here.

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So six, six six -0 zero two and we'll get the default file permission, as you can see over here,

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six, six, four.

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Now let's move on to the next slide here.

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So here we have another example here.

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In this example, I would like to change and set the new mask value to zero 0 to 6 for both.

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So let's do it for the directory and the file.

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So for the directory we start with the seven, seven, seven -0 to 6.

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We will get the value here 751.

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So let's analyze the, the new default permission here, the 751.

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So seven to the user here is read, write, execute the five here.

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This is for the group will be reading execute.

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And number one here we only have the execute permission now let's do it for file.

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So it will be six, six six -0 to 6 and we'll get the outcome here.

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As we can see here, 640.

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Let's analyze these three digits.

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So the six for the user read or write, the four here for the group will be read and zero will be other.

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So the other no permission because it's zero.

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There is one point I should maybe mention to you we should put into consideration for regular files.

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We don't get execute permission by default.

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For example, if we have a umask with 0 to 1.

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We and we would like to create a directory directory one or directory two permissions.

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So the result will be 777 -0 two one will give us 756.

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However, I just mentioned that for the directories.

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However for a file.

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So in this case for the file it would be 666 -0 two one minus any execute permission.

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So here you are not going to get the execute permission.

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So we'll get six, four, four.

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There is some cases for that.

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But in general I just explained to you how to do it, how to calculate and how to get the default value

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for the Umask.

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So here's a hint.

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If we reboot or off on the system here in our system.

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So the system is going to reset the umask to the default umask So assume that you change it to 0026.

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Then if you log out or reboot the system.

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So the system will automatically will reset it to 0022.

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So in this case, if you would like to save the default umask in the system and you don't like you don't

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like the system to change it back to the old permission or the old default umask so we can do it permanently

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and shell configuration file, we can do it.

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Either we can save it either under the dot bash RC or under the slash under directory slash ATC slash

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profile.

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And this is the file that we can add the our mask that we would like the system to save it.

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So that's conclude our session.

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Thank you and see you in the next lesson.