Unix file protection

This assumes that everyone already has access to the directory where myfile is located and its parent directories; that is, you must set the directory permissions separately. If you omit the access class, it's assumed to be all, so you could also enter the previous example as: For example, to remove read and write permission for group and other users leaving only yourself with read and write permission on a file named myfile, you would enter:

Unix file protection

To protect a file against accidental overwriting. If you enter a number with less than three digits as an argument to chmod, omitted characters are replaced with zeros starting from the left. There is actually a fourth digit on Linux systems, that precedes the first three and sets special access modes.

Change permissions for a file in Unix

Everything about these and many more are located in the Info pages. Logging on to another group When you type id on Unix file protection command line, you get a list of all the groups that you can possibly belong to, preceded by your user name and ID and the group name and ID that you are currently connected with.

However, on many Linux systems you can only be actively logged in to one group at the time. When initially connecting to the system, Unix file protection is the group that asim will belong to. User private group scheme In order to allow more flexibility, most Linux systems follow the so-called user private group scheme, that assigns each user primarily to his or her own group.

This group is a group that only contains this particular user, hence the name "private group".

ACL Entries for Directories

Usually this group has the same name as the user login name, which can be a bit confusing. Apart from his own private group, user asim can also be in the groups users and web. Because these are secondary groups to this user, he will need to use the newgrp to log into any of these groups use gpasswd for setting the group password first.

In the example, asim needs to create files that are owned by the group web. See the manpage for newgrp for more information. The file mask When a new file is saved somewhere, it is first subjected to the standard security procedure. Files without permissions don't exist on Linux. The standard file permission is determined by the mask for new file creation.

The value of this mask can be displayed using the umask command: In the example above, however, we see 4 values displayed, yet there are only 3 permission categories: The first zero is part of the special file attributes settings, which we will discuss in Section 3.

It might just as well be that this first zero is not displayed on your system when entering the umask command, and that you only see 3 numbers representing the default file creation mask.

Each UNIX-like system has a system function for creating new files, which is called each time a user uses a program that creates new files, for instance, when downloading a file from the Internet, when saving a new text document and so on.

This function creates both new files and new directories. Full read, write and execute permission is granted to everybody when creating a new directory. When creating a new file, this function will grant read and write permissions for everybody, but set execute permissions to none for all user categories.

This, before the mask is applied, a directory has permissions or rwxrwxrwx, a plain file or rw-rw-rw. The umask value is subtracted from these default permissions after the function has created the new file or directory.

Thus, a directory will have permissions of by default, a fileif the mask value is 0 This is demonstrated in the example below: If it wouldn't have that, it would not be accessible.

Try this out by chmodding a directory ! If you log in to another group using the newgrp command, the mask remains unchanged.

Unix file protection

Thus, if it is set tofiles and directories that you create while being in the new group will also be accessible to the other members of that group; you don't have to use chmod. The root user usually has stricter default file creation permissions: You can change them in your own shell configuration file, see Chapter 7 on customizing your shell environment.

Changing user and group ownership When a file is owned by the wrong user or group, the error can be repaired with the chown change owner and chgrp change group commands.

Changing file ownership is a frequent system administrative task in environments where files need to be shared in a group. Both commands are very flexible, as you can find out by using the --help option.Unix (/ ˈ j uː n ɪ k s /; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, development starting in the s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others.

The protection mechanism is the same for files as it is for directories so for this discussion the term object refers to either a file or a directory.

Access Modes: Read, Write, Execute Unix has three access modes: read, write, and execute.

ACL Entries for Files

File and Directory Ownership. Traditional UNIX file permissions can assign ownership to three classes of users: user – The file or directory owner, which is usually the user who created the file.

The owner of a file can decide who has the right to read the file, to write to the file (make changes to it), or, if the file is a command, to execute the file. Change permissions for a file in Unix.

You can change file permissions with the chmod command. In Unix, file permissions, which establish who may have different types of access to a file, are specified by both access classes and access timberdesignmag.com classes are groups of users, and each may be assigned specific access types.

Mar 16,  · Zip file with password protection I have read all or atleast most of the threads on the website, but couldn't come up with a solution. I am running ZIP version on HP-UX but I dont see the -P (password) option. Is there a way to protect a file in such a way that even root cannot delete it or rewrite it after creating it?

I have a file which is created by root under /var/log/ and I .

Change permissions for a file in Unix