Permissions Utilities (Demo)
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Video Transcription
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>> Hey, Cybrarians, welcome back to
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the Linux plus course here at Cybrary,
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I'm your instructor Rob Gills,
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and in this lesson we're going to
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be covering Permissions Utilities.
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Upon completion of today's lesson,
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you're going to be able to understand
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how permissions are modified.
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We're going to talk about how ownership is modified,
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and then we're going to use the commands: change mod,
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change own, and change group.
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First of all, permissions modifications
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are done with the change mode command,
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which I just say chmod [LAUGHTER].
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Now this command accepts
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octal or symbolic notation and
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>> we've talked about octal,
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>> for example, octal notation indicates that
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something that has read permissions
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>> has the number four.
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>> Something that has write permissions
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>> has the number two,
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>> and something has execute permissions
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>> has the number one.
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>> We can see for example,
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if we have a user with read and write
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and then group and other with just read,
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the permissions would be 644.
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But we can also use symbolic notation.
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Symbolic notation talks about user group other UGO and
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RWX to indicate permissions
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as well as A to change permissions for all.
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We could use plus to add these permissions,
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minus to remove permissions on the user group or owner,
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and we could use equal to set permissions,
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and we'll see all this in the demo later.
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For example, to set user owner to
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read and write in group or and other to
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just have read only on file.txt we can say
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change mode or chmod
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644 file.tex or we use a symbolic option.
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We can say change mode, user=rw,
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group and other only get r for read
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on file.txt and that's the same thing,
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>> works either way.
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>> Now if you want to modify
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the ownership on a file or directory object,
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we use the change owner command
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>> or I just call it chown.
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>> The chown command accepts the user and
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group owner separated by a colon or a period.
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Both are valid, so we can see
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chown user colon group or user dot group.
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Both of those work fine.
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You can also specify just the user owner
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>> or group owner.
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>> For example, we could say chown user file.txt
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or chown colon group file.txt.
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If you put a colon in front of the name,
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chown understands that we're changing
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the group if we don't put any colons there at all,
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it just assumes that we're changing the user owner.
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If we want to change the user
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owner and the group owner to be the
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same or the default group that is applied to the user,
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for example, my user account is
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Rob and I'm also have a group account called Rob.
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If I say chownrob colon file.txt,
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now that file is going to have rob,
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rob for the user owner and group ownership permissions.
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The very last command we're going to look at before we
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get into the demo is the change group command,
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and this command is used to change
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just the group that's
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assigned to a file or directory object.
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Chang group takes the name of
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the new group that we want on the object to change.
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For example, if you have a directory, directory one,
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we want to modify it by root
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so that the group ownership is changed,
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we could do that by just using change group.
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For example, is owned by me,
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so Rob's a user,
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Rob's a group owner directory one.
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We can say change group Engine X on directory one.
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Now if we look it again with ls dash l,
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we'll see Rob's the user owner,
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but engine X is the group owner on directory one.
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Let's take a little bit of a closer look at all of
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these commands with some demo time.
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Here we are back in our demo environment,
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and just so that we can do things a little bit faster,
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I'm going to go ahead and become
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root just so that
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we don't run into any issues running these commands.
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The first thing that we'll see if we do an ls dash l
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here is that we have a file called file.txt.
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This is the file that we're going to pick on
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all day-to-day in our demo.
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If we look at this,
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we can see that the permissions it currently
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has on file.txt are read write,
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read write and read.
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The way that we can change this is by setting
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the file permissions with
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change mode or chmod as I call it.
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For example, if we want to change
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everyone to be able to read or write to the file,
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we could do that with chmod
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and we can say 666 because remember,
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read plus write, four plus two is six on file.txt.
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But, just for purposes of illustration,
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let's do this instead of using app limitations.
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Let's use the symbolic notation because again,
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we want to set it to be read write,
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read write, read write for everybody.
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We could just say all equals rw on file.txt.
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Now when we do an ls dash l,
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we'll see that on file.txt,
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everyone has read write,
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read write and read write permissions.
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If we want to mess with this and say that we want
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to have the file executable,
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but have it only be able to be run by
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any user, for example,
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be able to be run as any user as me,
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we can mess with the SUID bit.
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We could say that we want to do change mode four,
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because that's the SUID bit, 766.
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Let's turn this into an executable
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and we'll do that on file.txt.
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Now if we do an ls dash l,
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what we'll see is that this file.txt
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has read write execute for
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users and any user will be able to
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execute it as me because of this s bit that's set there,
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and then everybody else can read and write.
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Now, if we want to change the object ownership,
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let's just make the user owner different.
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Right now, this user-owner setup is Rob.
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Let's go ahead and do it chown,
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and we can change the owner.
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Let's change the owner to route on file.txt.
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Let me do an ls dash l. We'll see that
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the user ownership has changed to root.
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If we want to change that to the group,
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we can do a chown colon group on file.txt,
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and now we do an ls dash l,
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and we'll see that the user and group
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have both been changed to root.
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If we want to set it up so that
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it is back to me as the group owner,
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we can use a change group command,
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chgroup and we'll set the user or set
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the group ownership back to Rob on file.txt.
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Now if we do an ls dash l,
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we can see that that is set back to
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your root Rob and file.txt.
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If we want to set everything back
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>> to just one user owner,
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>> we can do that whith chown Rob file.txt,
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and notice where I put the semicolon here or
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the colon here rather is after me.
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Now when we do an ls dash l,
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we'll see that Rob has the user
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and group ownership permissions on this file.
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We've also set this back so that
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it doesn't have the SUID bit.
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It's just back to 766 on this file.txt.
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One other thing that I should talk about real quickly,
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if we do a touch on,
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we'll do file test and we do an LL,
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we can see that on file.txt we have read write,
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read write and read permissions.
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If I become root and I do SUID bash,
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and I do touch file test two and do an LL,
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we can see that file test two gives read write,
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read, and read permissions,
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and that is because depending upon
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what user type you are,
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your permission is set differently.
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This is because of something called the UMASK.
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We're going to talk about that coming up
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pretty soon in the course.
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With that, we've reached the end of this lesson,
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and in this lesson, we covered
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how permissions are modified.
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We talked about changing ownerships and
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then also how to use the commands change mode,
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change own, and change group.
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Thanks so much for being here and I look
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forward to seeing you in the next lesson.
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