Due: October 19, 2016
This laboratory exercise is designed to teach you about Linux file permissions.
You are to write a program called “access” that will say what rights a user or group has over a file or directory.
access[ -g ] name file1 …In this command, name is either a name or a non-negative integer. If the -g flag is given, name is interpreted as a group name or GID, and if that flag is not given, it is interpreted as a user name or UID. It is an error to give a non-existent user or group name, but it is not an error to give a UID or GID without an associated name.
In these examples, “files” is a file and “dirt” is a directory. Assume “filex” has owner bishop, group owner users, and protection mode 0654, and the directory “dirx” has the same owner and group and the protection mode 0751. Then the command
access bishop filex
The user bishop (UID 7000403) can read and write the file filex
access sushi filex
The user sshd (UID 74) can read the file filex
and the command
access 10 filex
The user with UID 10 can read the file filex
but the command
access -g 10 filex
Members of the group users (GID 10) can read and execute the file filex
The difference is that, without the -g option, the 10 is interpreted as a UID, and there is no associated name. But with that option, the 10 is interpreted as a GID, and that has the associated name “users”.
If any of the named files are directories, you are to print “list the contents of”, “modify”, or “search” rather than “read”, “write”, and “execute”, respectively. So, the command
access bishop dirx
The user bishop (UID 7000403) can list the contents of, modify, and search the directory dirx
(all on the same line), the command
access -g users dirx
Members of the group users (GID 10) can list the contents of and search the directory dirx
and the command
access -g cosmos dirx
Members of the group cosmos (GID 900) can search the directory dirx
A reference version of this program is available in the directory ~bishop/ecs153; it is the executable file “access”. Your output, and especially your error output, is to match that of this program.
You must submit either a tar archive or a compressed tar archive to Canvas, as described in the handout All About Programs. Do this as follows:
When we grade your program, 40% of the grade will be based on robustness, which includes handling errors and problems gracefully as well as good programming style. If you lose points because of this, we will give you a week to modify your program and resubmit it. We will then regrade only the robustness, and add back 75% of the points you regain. So if your score on the robustness part is 20 out of 40, you can get up to 15 of the other 20 points back by fixing your program and resubmitting it.
|You can also obtain a PDF version of this.||Version of October 6, 2016 at 11:35PM|