CP367: Lab 03 - Winter 2026 - unix Commands II

Wildcards

Wildcards provide a shortcut for file handling in the bash shell. Wildcards can be used to match multiple filenames, making moves, copies, and deletions less work. The wildcard characters are:

Finding and Identifying Files

file

The file command helps you identify files for type and purpose, as in these examples:

/home/dbrown> file CP367/ctest
CP367/ctest: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs),
for GNU/Linux 2.6.32, BuildID[sha1]=e9a5ffe3f20638c014cff096402e09bba16d68fa, not stripped
/home/dbrown> file CP367/ctest.c
CP367/ctest.c: C source, ASCII text
/home/dbrown> file CP367
CP367:          directory

find

The find allows you to search for files by file name, type of file, directory, or even file size. It automatically searches subdirectories of the start directory you name. The command skeleton is:

find directory -name "targetfile" -type type -size size -mtime time -ls

(There are more options, but these are a good start.)

Examples:

find has numerous other options - use man find to see more.

Permissions

Last week you looked briefly at the output of the ls -l command. the first ten characters of the long listing gave information about file types and permissions. The first character notes the file type, and the next nine characters identify the file permissions. A file permission simply tells the unix system whom is allowed to read, write, or execute a file.

The nine characters are divided up into three groups of three characters each. The three areas of permission (in order from left to right) are:

• owner: the creator of the file - i.e. you
• group: the group the owner belongs to - this group is also noted in the long listing, and on hopper is the student group
• other: everyone on the unix system who is not the file's owner or a member of the file's group

Each group of three permissions has three characters. These characters represent the following permissions, in order:

• read: r allows read permission for the permission area
• write: w allows write permission for the permission area
• execution: x allows execution permission for the permission area

Examples:

Read, write, and execute permission for the owner

Changing Permissions

File and directory permissions are changed with the chmod command. chmod (change mode) is a complex command, and you are welcome to use it in any way you understand, but we will show you one simple way to use it. The command skeleton is:

chmod [-R] who[+/-/=]permissions file

• -R: [optional] recurse into subdirectories - changes permissions in the current directory and any subdirectories it contains
• who : set permissions for the owner, group, or other. The options are:

  chmod Options

  Code	Meaning
  u	The file owner
  g	The group
  o	All other users
  a	All of the above

• permissions : the read, write, and execute permissions to set:

  chmod Permissions

  +r / -r	add (+) / remove (-) read permissions
  +w / -w	add (+) / remove (-) write permissions
  +x / -x	add (+) / remove (-) execution permissions

chmod Permission Examples

Processes

A process (or thread) represents CPU time and calculation resources that are allocated to a program when that program is executed. A multi-processor, multi-user machine such as hopper may support tens of thousands of simultaneous processes. Generally individual users have a limit to the number of processes they may run (256, for example), because despite having such a large number of available processes, very clever (or very stupid) users can bring a unix machine to its knees by using up all of the available processes.

Processes are numbered. Using this number, you can determine when a process was started, how much CPU time it is using, and what its parent process is, if any.

The ps (Process Status) Command

The ps command lists running processes, and in particular tells you process numbers. This is important, because once you know a process number you can kill the process if it is a runaway process. The ps -f command displays information like this:

/home/dbrown> ps -f
UID         PID   PPID  C STIME TTY          TIME CMD
dbrown    46379  24231 99 12:40 pts/1    00:01:09 ./ouch
dbrown    46482  24231 99 12:42 pts/1    00:00:15 ./ouch
dbrown    39286  39283  0 16:11 pts/1    00:00:00 -bash
dbrown    46452  39286  0 17:40 pts/1    00:00:00 emacs CP367/ctest.c
dbrown    46506  39286  0 17:41 pts/1    00:00:00 ps -f

The useful parts of the ps -f output are:

UID

Your user id.

PID

The process ID of the listed process.

PPID

The parent process of the listed process.

STIME

The process start time.

TIME

The cumulative execution time for the process.

CMD

The command that started the process.

This sample output tells us a number of things:

• The user dbrown is using the bash shell, and running emacs, and has a couple versions of the program ouch running. The ./ in front of the ouch command means it is very likely that these are programs written by the user and being run from a user's directory.
• The bash process is the parent process for the ps and emacs commands. The ouch processes are running under the parent process 24231, which is a different parent process, implying that they were started in an different session.
• None of the ps, bash, or emacs commands are using any significant time resources on the server. The ouch commands, on the other hand, are, as the TIME field shows.
• The start times for the ouch commands come before the start time for the current bash session. This implies that the ouch commands are left over from the user's previous on-line session, and therefore must be runaway processes. These runaway processes should be killed.

To see only the processes owned by a particular user, generally yourself, enter:

ps -fu login

Thus, to list only the processes owned by the dbrown account, enter:

ps -fu dbrown

The kill (Terminate Process) Command

The kill command allows you to terminate processes that you own. You may kill an individual process or a parent process. Killing a parent process kills all child processes. Although there are various forms of the command, kill -9 PID is typically used. To kill the emacs process listed above (id: 46452), for example:

/home/dbrown> kill -9 46452
/home/dbrown> ps -f
UID         PID   PPID  C STIME TTY          TIME CMD
dbrown    46379  24231 99 12:40 pts/1    00:03:25 ./ouch
dbrown    46482  24231 99 12:42 pts/1    00:02:32 ./ouch
dbrown    39286  39283  0 16:11 pts/1    00:00:00 -bash
dbrown    46659  39286  0 17:43 pts/1    00:00:00 ps -f
[2]+  Killed                  emacs CP367/ctest.c

Attempting to kill a process you do not own fails with an error message:

/home/dbrown> kill -9 1
-bash: kill: (1) - Operation not permitted

Upon occasion, child processes either cannot be killed or have sibling processes automatically spawned by a parent process for reasons that we will not go into. Killing the parent process kills the children and the spawning. Be cautious with this, however. The following command successfully kills the parent (id: 39286) of the emacs process:

/home/dbrown> kill -9 39286

but because it is the bash shell process, you have just killed the shell and closed your connection.

1. Get a partner. Try to access one of your partner's directories using ls . What happens?

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2. Both your and your partner change permissions on one of your existing directories. What do you have to do to allow your partner to see the contents of your directories, and visa-versa?

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3. Both your and your partner change permissions on one of your existing directories. What do you have to do to allow your partner to create a file in one of your directories, and visa-versa?

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4. Attempt to delete a file that your partner created in your directory. How's that working for you?

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