Red Hat NETSCAPE MANAGEMENT SYSTEM 6.0 - CUSTOMIZATION Instrukcja Użytkownika Pobierz pdf (Strona 257)

16.12 Ownership and Permissions 245

That was one demonstration of Linux’s security features. Linux, like UNIX, is a multi-user system,

and ﬁle permissions are one way the system uses to protect against any type of tampering – malicious

or accidental.

One way to gain entry when we see we’re denied permission is to su to root, as we learned earlier.

That’s because whoever knows the root password has complete access.

[billy@localhost billy]$ su root

Password: (your root password)

[root@localhost billy]# cd /root

[root@localhost /root]#

But switching to superuser isn’talwaysconvenient– or smart, since it’s so easy to mistakenly mess

up important conﬁguration ﬁles.

All ﬁles and directories are “owned” by the person who created them. We created the ﬁle sneak-

ers.txt in our login directory, so sneakers.txt “belongs” to us.

That means, we can specify who’sallowedtoreadtheﬁle, write to the ﬁle or, if it were an application

instead of a text ﬁle, who can execute the ﬁle.

Reading, writing and executing are the three main settings in permissions.

Since every user on the system is placed into a group when that user is created, then we can also

specify whether certain groups can read, write to, or execute our ﬁle.

Let’s take a closer look at sneakers.txt with the ls command using the -l (long) option (see

Figure 16.16).

[billy@localhost billy]$ ls -l sneakers.txt

-rw-rw-r-- 1 billy billy 150 Mar 19 08:08 sneakers.txt

There’s quite a bit of detail here. We can see who can read (r)andwriteto(w)theﬁle,aswellaswho

created the ﬁle (billy) and to which group the owner belongs (billy).

Tip: Remember that, by default, your group was the login name you chose.

Other information to the right of the group includes the ﬁle name, date and time of its creation as

well as size.

How do all those dashes and letters ﬁttogether?It’s not as hard to read as it might seem. Let’s take

a look:

-rw-rw-r--

1 2 ... 252 253 254 255 256 257 258 259 260 261 262 ... 299 300

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