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
| 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. |
| 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:
Table 3-11. File permissions
| Who\What | r(ead) | w(rite) | (e)x(ecute) |
|---|---|---|---|
| u(ser) | 4 | 2 | 1 |
| g(roup) | 4 | 2 | 1 |
| o(ther) | 4 | 2 | 1 |
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