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2. File Basics tinguish between three user categories: the owner of the file, every user who is a member of the group associated with the file (also called the owner group) but who is not the owner, and others, which includes every other user who is neither the owner nor a member of the owner group. There are three different permissions: 1. Read permission (r): enables a user to read the contents of a file. For a directory, the user can list its contents (i.e. the files in this directory). 2. Write permission (w): allows modification of a file’s content. For a directory, the write permission allows a user to add or remove files from this directory, even if he is not the owner of these files. 3. eXecute permission (x): enables a file to be executed (normally only executable files have this permission set). For a directory, it allows a user to traverse it, which means going into or through that directory. Note that this is different to the read access: you may be able to traverse a directory but still be unable to read its content! Every permission combination is possible. For example, you can allow only yourself to read the file and forbid access to all other users. As the file owner, you can also change the owner group (if and only if you’re a member of the new group). Lets take the example of a file and a directory. The display below represents entering the ls -l command from the command line: $ ls -l total 1 -rw-r—–1 queen users 0 Jul 8 14:11 a_file drwxr-xr–2 peter users 1024 Jul 8 14:11 a_directory/ $ The results of the ls -l command are (from left to right): The first ten characters represent the file’s type and the permissions associated with it. The first character is the file’s type: if it’s a regular file, you will see a dash (-). If it’s a directory, the leftmost character will be a d. There are other file types, which we’ll discuss later on. The next nine characters represent permissions associated with that file. The nine characters are actually three groups of three permissions. The first group represents the rights associated with the file owner; the next three apply to all users belonging to the owner group; and the last three apply to others. A dash (-) means that the permission is not set.

2. File Basics to enter your password. Like the graphic mode login, the console login will not echo the characters you are typing on the screen, but there will be no stars either. Note that you can log in several times with the same account on additional consoles and under X. Each session you open is independent of the others, and it is even possible to open several X sessions at the same time (although this is not recommended since it consumes a lot of resources). By default, Mandriva Linux has six virtual consoles in addition to the one reserved for the graphical interface. You can switch to any of them by pressing the Ctrl Alt F key sequence, where is — the number of the console that you want to switch to. By default, the graphical interface is on console number 7. Therefore, to switch to the second console, you would press the Ctrl , Alt and F2 keys. During the installation, DrakX also prompted you for the password of a very special user: root. This is the system administrator who will most likely be yourself. For your system’s security, it is very important for the root account to be always protected by a good and hard-to-guess password! If you regularly log in as root, it can be very easy to make a mistake which could render your system unusable: one single mistake can do it. In particular, if you did not set a password for the root account, then any user can alter any part of your system (and even other operating systems on your machine!). Obviously this is not a good idea. It is worth mentioning that internally, the system does not identify you by your login name. Instead, it uses a unique number assigned to the name: the User ID (UID) . Similarly every group is identified by its Group ID (GID) and not by its name. 2. File Basics Compared to Windows and most other operating systems, files are handled very differently under GNU/Linux. In this section we will cover the most obvious differences. For more information, please read Chapter 30, The Linux File System [407]. The major differences result directly from the fact that Linux is a multiuser system: every file is the exclusive property of one user and one group. One thing we didn’t mention about users is that every one of them possesses a personal directory (called the home directory). The user is the owner of this directory and all files created in it. Also note that these have an associated group as well and it is the primary group that the user belongs to. As it was mentioned before (see Section 1, Users and Groups [381]), a user may be in more than one group at the same time. However, this would not be very useful if that were the only notion of file ownership. As the file owner, a user may set permissions on files. These permissions dis

1. Users and Groups Figure 27.1. Graphical Mode Login Session In order to log in, you must first select your account from the list. A new dialog will be displayed, prompting you for your password . Note that you will have to type in your password blindly, because the characters will be echoed on screen as stars (*) instead of the characters you type in the password field. You may also choose your session type (window manager). Once you’re ready, press the Login button. If you are in console or text mode, you will be presented with something similar to the following: Mandriva Linux release 2006.0 (CodeName) for i586 Kernel 2.6.12-6mdk on an i686 / tty1 [machine_name] login: To log in, type your login name at the login: prompt and press Enter . Next, the login program (called login) will display a Password: prompt and wait for you

Chapter 27. Basic UNIX System Concepts The name UNIX may be familiar to you. You may even use a UNIX system at work, in which case this chapter may be of less interest. For those of you who have never used a UNIX system, reading this chapter is absolutely necessary. Understanding the concepts which will be introduced here will answer a surprisingly large number of questions commonly asked by beginners in the GNU/Linux world. Similarly some of these concepts will likely help you solve many of the problems you may encounter in the future. 1. Users and Groups Since they have a direct influence on all other concepts, this section will introduce the concepts of users and groups which are extremely important. Linux is a true multiuser system, and in order to use your GNU/Linux machine, you must have an account on the machine. When you created a user during installation, you actually created an account. In case you don’t remember, you were prompted for the following items: the user’s real name (which could actually be whatever you want); a login name; and a password. The two most important parameters here are the login name (commonly abbreviated to login) and the password. You must have both of these in order to access the system. When you create a user, a default group is also created. Later on, we will see that groups are useful when you want to share files with other people. A group may contain as many users as you wish, and it is very common to see such a separation in large systems. For example, at a university, you could have one group per department, another group for teachers, and so on. The opposite is also true: a user may be a member of one or more groups. A math teacher, for example, could be a member of the teachers’ group and also of his math students’ group. Now that we’ve covered the background information, let us look at how to actually log in. If the graphical interface is automatically started on boot up, your start-up screen will look like Figure 27.1, Graphical Mode Login Session [382].

Then we tackle the command-line interface (Chapter 33, Introduction to the Command Line [441]). We discuss file-handling utilities such as the mkdir and touch commands, and how to move, delete and copy files and directories in the file system. We also speak about file attributes and how to handle them with commands such as chown and chgrp. We then tackle shell globbing patterns, redirections and pipes, command-line completion, as well as basic job(s) control. The next chapter covers text editing (Chapter 34, Text Editing: Emacs and VI [455]). As most UNIX configuration files are text files, you will eventually want or need to edit them in a text editor. You will learn how to use two of the most famous text editors in the UNIX and GNU/Linux worlds: the mighty Emacs, written by Richard M. Stallman, and good-old Vi, written in 1976 by Bill Joy. You should then be able to perform basic maintenance on your system. The following two chapters present practical uses of the command line (Chapter 35, Command-Line Utilities [467]), and process control (Chapter 36, Process Control [487]) in general. The next chapter (Chapter 37, The Start-Up Files: init sysv [493]) presents the Mandriva Linux boot-up procedure, and how to use it efficiently. We talk about init (the process which allows your system to boot) and different run levels you may wish to use (especially for maintenance tasks). We also briefly explain how to use drakxservices to manage services (see Section 2, Configuring Start- Up Services [276], for more details). Next we explain how to securely access a remote system (with ssh) to perform maintenance tasks, to run programs on it, and more (Chapter 38, Secure Remote Access [497]). We give you a quick overview of the connection scheme and then we describe a basic server/client ssh setup. We also discuss the usage of scp. We close out this book with a chapter dedicated to package management using the command line (Chapter 39, Package Management From The Command Line [501]). In it we show you how to use the urpmi utility along with its counterpart, urpme. We also explain how to manage media sources.

Part 6. Introduction to Linux Command-Line Basics The following parts of the manual are aimed at those wishing to better understand their Mandriva Linux system, and who want to exploit its huge capabilities. After reading them, we hope that you will be at ease with daily administration of a GNU/Linux box. Here’s an overview of the parts it contains, along with a brief description of each chapter. In the first part we introduce you to the GNU/Linux system. We discuss its architecture, the main file systems available and some of the more peculiar aspects such as the /proc file system. In Chapter 27, Basic UNIX System Concepts [381] we talk about the UNIXparadigm while speaking more specifically of the GNU/Linux world. We discuss the standard file-manipulation utilities as well as some useful features provided by the shell. Then comes a complementary chapter (Chapter 28, Disks and Partitions [395]) in which we explain how hard disks are managed under GNU/Linux. We also deal with hard disk partitioning. We explore the organization of the file tree in Chapter 29, File-Tree Organiza tion [401]. UNIX systems tend to grow very large, but every file has its place in a specific directory. After reading this chapter, you will know where to look for files depending on their role in the system. The next chapter deals with file systems (Chapter 30, The Linux File System [407]). After a presentation of the available ones, we discuss file types and additional concepts and utilities such as inodes and pipes. The following chapter (Chapter 31, The /proc File System [421]) introduces a special (and virtual) GNU/Linux file system called /proc. The second part (Linux in Depth [431]) deals with more practical topics. We talk about the relationship between file systems and mount points, how to use the command line in your daily tasks, how to edit configuration files with light and powerful editors, and more. We cover the topics of file systems and mount points (Chapter 32, File Systems and Mount Points [433]) by defining both terms, as well as explaining them with real life examples.

13.4. Directly Contacting the Person in Charge 13.4. Directly Contacting the Person in Charge Use this option as a very last resort and in really extreme situations unless you want to offer your collaboration! Software developers generally receive mountains of e-mails, so your anguished question on the use of the cd command will most likely… be ignored! The addresses will be found either on the home page of a project’s site or in the software documentation. A last word: do not underestimate your neighbors’ skills or those of your local LUG (Linux Users Group). And please, do not throw your computer through the window. If your problem isn’t fixed today, it may be tomorrow… 13.5. Mandriva Business Services Finally, when facing a really challenging situation, corporate users (especially) might consider hiring one of Mandriva’s consultants to address their specific needs. This is one of the strong suits of open-source products: we have the source, we have the power! Therefore, almost any problem, no matter how complex, specific or high level, may be solved right in the heart of the software. You might also want to customize your Linux environment to meet very precise goals. For example, you could use Mandriva Linux as a custom routing application on special devices. Know that Mandriva consulting services [http://www. mandriva.com/enterprise/products/] can help you. 14. Final Thoughts As you have seen there are many more ways to recover from an emergency than 4 by re-installing the whole system again. Sure, you need a little expertise in applying some of the techniques described in this chapter, but with a little practice you will gain such expertise. However, we hope that you will never need to really master these techniques … although it does not hurt to know them. We hope that the instructions and examples given will be useful when you are in need. Good luck recovering from an emergency! The usual way to fix things in some other operating systems…

13.1. Search the Internet 13.1. Search the Internet The various Internet sites previously mentioned are excellent starting points. They deal with general and very specific aspects of your potential problems. Finally, try a general search engine such as Google or, as mentioned above, the Linux-specific Google search engine. And do not hesitate to use the Advanced search [http:// www.google.com/advanced_search] option with very detailed questions, such as the error message you are receiving. 13.2. Mailing Lists and Newsgroups Archives The previous searches may lead you to general answers which hide the results of your specific question amongst many other answers. To refine your search, you can try the following. First, try to find a list which seems specifically geared to your problem, then perform a search in its archive pages. Example You’ve noticed some strange behavior while trying to use GRUB with a minix partition. One of the results of a search using the grub mailing list keywords in Google is a link to the GRUB mailing list archive [http://mail.gnu.org/archive/html/bug-grub/]. It even offers a search engine, which when searched for Minix leads you directly to a patch. Note that not all archives have an embedded search en gine. However, using Google as an example, you can easily use the advanced field domain to limit your search to the specific site hosting the archive. This strategy may also be used to exclude sites which keep returning garbage. For a newsgroups search, Google Groups [http://groups.google.com/] maintains an archive of an amazingly large number of newsgroup channels. 13.3. Questions to Mailing Lists and Newsgroups See the related sections above: Section 11.1, Mailing Lists [375] and Section 11.2, Newsgroups [376]. Reading How To Ask Questions The Smart Way [http:// www.catb.org/~esr/faqs/smart-questions.html] may be of great help.

11.2. Newsgroups Mailing lists usually have archives: check them out! Your question may have been debated just before you subscribed to the list; 11.2. Newsgroups Before asking for help on newsgroups, it is advisable to find out if your problem has already been covered (or solved) on Google Groups [http://groups.google. com/]. If nothing is relevant to your question, then go to a newsgroup entirely devoted to Mandriva Linux [news:alt.os.linux.mandriva]. You may also join many other groups in the comp.os.linux.* hierarchy : comp.os.linux.setup [news:comp.os.linux.setup]: questions about Linux configuration (devices, configuration of applications) and resolution of miscellaneous problems. comp.os.linux.misc [news:comp.os.linux.misc]: whatever doesn’t fit in any other group. and others… Before posting to one of these groups, make sure you have done your homework and read the available documentation on your specific issue. If you have not, you will most likely get the following answer: RTFM. And nothing more! 12. Mandriva Linux’s Specific Troubleshooting Tools Each administration tool (the ones started from Mandriva Linux Control Center) is a potential trouble fixing tool. You can use all these tools to revert configuration changes, to add or remove software, to update your system with the latest fixes from Mandriva, etc. If you think you have found a bug in any of our tools, please feel free to submit a bug report using Drakbug, our automated bug report tool, see Section 3, The Drakbug Reporting Tool [206] for more information. 13. General Guidelines for Solving a Problem under Mandriva Linux Here are the different means available to you in your problem-solving quest. Try the first option and only then, if that does not work, try the second, and so on.

11. Troubleshooting Documentation Resources Once this operation is completed, your floppy boot disk will be ready for use. Replace /dev/fd0 with /dev/fd1 if you are using the second floppy drive and, of course, the name of the image with the one you want. 4. If you want to create a USB boot key, connect an empty USB key to the machine and type: dd if=/mnt/cdrom/install/images/all.img of=/dev/sdb Replace /dev/sdb by your USB key’s device name. Once this operation is done, your USB boot key will be ready for use. 11. Troubleshooting Documentation Resources 11.1. Mailing Lists Mailing lists still remain very popular in spite of the multiplicity of other means of communication. Almost every piece of GNU/Linux software has its own mailing list geared towards users, developers, announcements, etc. You can also consult the mailing lists of Mandriva Linux-related project [http:// www.mandriva.com/community/resources/newsgroups]. We cannot give you a complete list of addresses but bear in mind that it’s quite often the best means to get in touch with the top experts on a particular subject. Some advice, however: Don’t post questions which are off topic. Carefully read the guidelines which are often sent when you first subscribe or where you found the address of the list. We also recommend that you read the E-mail Etiquette [http://www. iwillfollow.com/email.htm] also known as the Netiquette, which will give you a few hints on getting started. If you have spare time, you may also consider reading the corresponding RFCs [http://www.rfc-editor.org/]. IMPORTANT: remember to always keep the first e-mail you receive from a mailing list since it normally tells you how to unsubscribe if you end up needing to leave the list; Respect the general rules applicable to e-mail: in particular, do not send HTML messages: text only;