Exercise 2

System Calls

In this exercise, we will gather information about the following commands:

rm, mv, chmod, chown, mkdir, rmdir, kill, ln, sleep, wget

(You might need to install wget on your machine.)

Description

Command	Description
rm	remove files or directories
mv	move (rename) files
chmod	change file mode bits
chown	change file owner and group
mkdir	make directories
rmdir	remove empty directories
kill	send a signal to a process
ln	make links between files
sleep	delay for a specified amount of time
wget	non-interactive network downloader

Path

Installation path using the which command:

Command	Path
rm	/usr/bin/rm
mv	/usr/bin/mv
chmod	/usr/bin/chmod
chown	/usr/bin/chown
mkdir	/usr/bin/mkdir
rmdir	/usr/bin/rmdir
kill	/usr/bin/kill
ln	/usr/bin/ln
sleep	/usr/bin/sleep
wget	/usr/bin/wget

(Programs in /bin and /usr/bin are part of the base installation of the operating system.)

Example

Command	Example
rm	rm testfile.txt
mv	mv oldfile.txt newfile.txt
chmod	chmod 755 script.sh
chown	chown user:group file.txt
mkdir	mkdir newdir
rmdir	rmdir olddir
kill	kill 1234
ln	ln -s /path/to/original /path/to/link
sleep	sleep 10
wget	wget http://example.com/file.txt

Characteristic System Calls

The system calls can be displayed using the following commands:

• ktrace and kdump (BSD)

• strace (Linux)

The characteristic system calls usually appear relatively near the end of the output because libraries are loaded and conditions are checked beforehand.

Command	System Calls
rm	unlink() (files), rmdir (empty directories)
mv	rename() (source and destination on the same filesystem), link/unlink (across different filesystems)
chmod	chmod()
chown	chown()
mkdir	mkdir()
rmdir	rmdir()
kill	kill()
ln	link (for hard links), symlink (for symbolic links)
sleep	nanosleep()
wget	socket(), connect()