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Linux system administration

Because we believed from the outset that we are in book is a personal computer, must be given some attention problems of Linux server administration. After all, you will not have Linux system Administrator, to turn to when faced with any problem. I want only the very beginning recall that, in most cases, to configure the system must have root access to root.

And one more preliminary remark, which help you better understand and master the principles of administration Linux: Any configuration of the OS can be performed by editing script files (or scripts), and configuration files read scripts. And those and others (ie, scripts, and configuration files) are simple text files. Of course, in Linux there are various special tools configuration and Linux systems administration (such as linuxconf or printtool), but the results of these programs still recorded in the same configuration files. Figuratively speaking, about Linux (and UNIX in general) can say "this is almost entirely processor text. If from the outset to remember about this features can be much easier to learn the issues of Linux remote administration and Linux network administration.

The way, if you want to simplify your work editing configuration files, immediately after the installation of OS Linux install Midnight Commander. This significantly facilitate your search and editing configuration files, as you can use built-in editor of the program (not to mention the fact that the search for the file you want too much easier).

The main tasks of the system administration. Processes and their IDs

The responsibilities of system administrator usually include the following tasks:

• Connection and configure the hardware devices;
• Install and update software;
• Launch and configure system-wide services (configuration system);
• User management
• Process management;
• Allocation of resources;
• Security.

Issues connecting and configuring hardware tools and procedures for installing and updating software ensure we consider in the next two chapters. Other problems system administration will be briefly discussed in this section. We begin by considering how the boot process is OS. The fact that this phase largely determines the mode of follow- of the system and its configuration. If you are able to influence the process BitTorrent, then you already can achieve the desired configuration system after downloading.

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But to understand the procedure, the bootstrap must have the most general idea of what a process system, since this concept will be constantly used in later.

In the first approximation we can assume that process - it is loaded into the RAM program. But this is not exactly correct to say that "the process executes the program. " The fact that Linux first start the process, which loads into memory the program from the specified file, and it begins to implement it. This means that each process must be started (as they say - "Generated") by some other process. That is, for each process is uniquely determined by its "parent" (or "Ancestor"), for which this process is a "child" (Or "descendant"). If you want to see the "tree" running processes on your system, run pstree . The output of this command allows you to see that the "father" of all processes in the system (or "tree root processes) is the process init , which first started after booting the kernel.

Each process in the system has a unique ID - PID, appointed by the process at startup. The process with ID 1 performs a program init . It is for this ID system distinguishes processes. Each running process at any time is in one of the following states: active (R), suspended (T) or "asleep" (S). The current state of the process is called the status of the process.

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Also identifier and status for each process in the special structure of the kernel saves the following (The following list is far from complete):

• Full command line to process tasks performed;
• Information about the process's allocated address space;
• Link to the current working directory and root directory of the process (The latter serves to limit access of the file structure);
• Table open process files
• So-called process environment, ie, list specified for the process variables with their current values;
• Attributes that define the rights and privileges of the process,
• Table of signal handlers;
• Indication of the parent process;
• User mask (umask) or access mask - indication of what rights should be removed when creating a new file or directory from the standard set of rights assigned to the file (Catalog).

Since Linux - system tasking, can be simultaneously running many processes. Incidentally, the word "simultaneously" is used not correct, because in fact at a time runs only one process. ( For accuracy it should be noted in multiprocessor systems, on which Linux can work can be performed simultaneously by several processes, but we consider only uniprocessor systems ). Planner processes allocated to each process a small quantum of time and After this quantum transfers control to the next process. Time slice allocated to each process, so small that Users create the illusion of simultaneous execution of many processes. And to some of the most important processes, receive more CPU time for each process set priority.

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users can "communicate" with processes by sending them signals. The processes also communicate with each another through signals. When we press the key combination >+< C > , to complete a program, we actually send respective process signal "Shut." In conclusion, the process sends a signal to the parent process of its completion. However, there are cases when the parent process ends earlier child. Processes that do not have a parent called "Orphans". "Orphans" are adopted automatically process init , who picks up signals on their completion. If the process is the parent for some reason can not receive a signal of the completion of a child process, then the child process is transformed into "zombies" and acquires the status of Z. Zombie process does not take up the CPU time (Ie, their execution is terminated), but the corresponding nuclear structure is not exempt. Destruction of such processes - One of the responsibilities of system administrator. Finally, the process may be a long time "to fall asleep, which can not interrupt. The status of such processes is denoted by D. Delete them can only when you restart the system.

special type of processes are the demons. Actually There is nothing special. This is just the processes that run in background, without displaying any data to the terminal. Demons typically used to perform service functions, service requests from other processes, not necessarily running on this computer.

must not forget that the processes can run ("Inside"), the separate threads (thread), or streams. Threads - a parallel run of one program, which are implemented as Linux processes that run with a special flag. From the standpoint of the system, they differ from other processes only because they do not create a separate environment, they executed from within the parent process.

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