Summary from the Introduction to Linux by OnWorks

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3.5. Summary‌

On UNIX, as on Linux, all entities are in some way or another presented to the system as files with the appropriate file properties. Use of (predefined) paths allows the users and the system admin to find, read and manipulate files.

We've made our first steps toward becoming an expert: we discussed the real and the fake structure of the file system, and we know about the Linux file security model, as well as several other security precautions that are taken on every system by default.

The shell is the most important tool for interaction with the system. We learned several shell commands in this chapter, which are listed in the table below.

Table 3-10. New commands in chapter 3: Files and the file system

Command	Meaning
bash	GNU shell program.
cat file(s)	Send content of file(s) to standard output.
cd directory	Enter directory. cd is a bash built-in command.
chgrp newgroup file(s)	Change the group ownership of file(s) to newgroup
chmod mode file(s)	Change access permissions on file(s)
chown newowner[:[newgroup]] file(s)	Change file owner and group ownership.
cp sourcefile targetfile	Copy sourcefile to targetfile.
df file	Reports on used disk space on the partition containing file.
echo string	Display a line of text
export	Part of bash that announces variables and their values to the system.
file filename	Determine file type of filename.
find path expression	Find files in the file system hierarchy
grep PATTERN file	Print lines in file containing the search pattern.
head file	Send the first part of file to standard output
id	Prints real and effective user name and groups.
info command	Read documentation about command.
less file	View file with a powerful viewer.
ln targetfile linkname	Make a link with name linkname to targetfile.
locate searchstring	Print all accessible files matching the search pattern.
ls file(s)	Prints directory content.
man command	Format and display online (system) manual pages for command.
mkdir newdir	Make a new empty directory.
mv oldfile newfile	Rename or move oldfile.
newgrp groupname	Log in to a new group.
pwd	Print the present or current working directory.

quota	Show disk usage and limits.
rm file	Removes files and directories.
rmdir file	Removes directories.
tail file	Print the last part of file.
umask [value]	Show or change new file creation mode.
wc file	Counts lines, words and characters in file.
which command	Shows the full path to command.

We also stressed the fact that you should READ THE MAN PAGES. This documentation is your first-aid kit and contains the answers to many questions. The above list contains the basic commands that you will use on a daily basis, but they can do much more than the tasks we've discussed here. Reading the documentation will give you the control you need.

Last but not least, a handy overview of file permissions: