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我们会通过消息、邮箱等方式尽快将举报结果通知您。Chapter 1. GNU/Linux tutorials
I think learning a computer system is like learning a new foreign language.
Although tutorial books and documentation are helpful, you have to practice it yourself.
In order to help you get started smoothly, I elaborate a few basic points.
The powerful design of
/ comes from the
operating system, i.e., a ,
operating system.
You must learn to take advantage of the power of these features and similarities between Unix and GNU/Linux.
Don't shy away from Unix oriented texts and don't rely solely on GNU/Linux texts, as this robs you of much useful information.
If you have been using any
system for a while with command line tools, you probably know everything I explain here.
Please use this as a reality check and refresher.
with the display manager such as gdm3. Suppose your hostname is foo, the login prompt looks as follows.
foo login:
If you did install a
environment such as
or , then you can get to a login prompt by Ctrl-Alt-F1, and you can return to the GUI environment via Alt-F7 (see
below for more).
At the login prompt, you type your username, e.g. penguin, and press the Enter-key, then type your password and press the Enter-key again.
Following the Unix tradition, the username and password of the Debian system are case sensitive.
The username is usually chosen only from the lowercase.
The first user account is usually created during the installation.
Additional user accounts can be created with adduser(8) by root.
The system starts with the greeting message stored in "/etc/motd" (Message Of The Day) and presents a command prompt.
Debian GNU/Linux jessie/sid foo tty1
foo login: penguin
Last login: Mon Sep 23 19:36:44 JST 2013 on tty3
Linux snoopy 3.11-1-amd64 #1 SMP Debian 3.11.6-2 () x86_64
The programs included with the Debian GNU/Linux syst
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Now you are in the . The shell interprets your commands.
with a display manager such as 's gdm3 by selecting "Desktop environment" task during the installation, you are presented with the graphical login screen upon starting your system.
You type your username and your password to login to the non-privileged user account.
Use tab to navigate between username and password, or use the mouse and primary click.
You can gain the shell prompt under X by starting a x-terminal-emulator program such as gnome-terminal(1), rxvt(1) or xterm(1).
Under the GNOME Desktop environment, clicking "Applications" → "Accessories" → "Terminal" does the trick.
You can also see the section below .
Under some other Desktop systems (like fluxbox), there may be no obvious starting point for the menu.
If this happens, just try (right) clicking the background of the desktop screen and hope for a menu to pop-up.
or privileged user.
From this account, you can perform the following system administration tasks.
Read, write, and remove any files on the system irrespective of their file permissions
Set file ownership and permissions of any files on the system
Set the password of any non-privileged users on the system
Login to any accounts without their passwords
This unlimited power of root account requires you to be considerate and responsible when using it.
Never share the root password with others.
File permissions of a file (including hardware devices such as CD-ROM etc. which are just another file for the Debian system) may render it unusable or inaccessible by non-root users.
Although the use of root account is a quick way to test this kind of situation, its resolution should be done through proper setting of file permissions and user's group membership (see ).
Never start the X display/session manager under the root account by typing in root to the prompt of the display manager such as gdm3(1).
Never run untrusted remote GUI program under X Window when critical information is displayed since it may eavesdrop your X screen.
character consoles available to start the command shell directly on the Linux host.
Unless you are in a GUI environment, you can switch between the virtual consoles by pressing the Left-Alt-key and one of the F1 — F6 keys simultaneously.
Each character console allows independent login to the account and offers the multiuser environment.
This multiuser environment is a great Unix feature, and very addictive.
If you are under the X Window System, you gain access to the character console 1 by pressing Ctrl-Alt-F1 key, i.e., the left-Ctrl-key, the left-Alt-key, and the F1-key are pressed together.
You can get back to the X Window System, normally running on the virtual console 7, by pressing Alt-F7.
You can alternatively change to another virtual console, e.g. to the console 1, from the commandline.
in memory for improved performance, the Debian system needs the proper shutdown procedure before power can safely be turned off. This is to maintain the integrity of files, by forcing all changes in memory to be written to disk. If the software power control is available, the shutdown procedure automatically turns off power of the system. (Otherwise, you may have to press power button for few seconds after the shutdown procedure.)
You can shutdown the system under the normal multiuser mode from the commandline.
# shutdown -h now
You can shutdown the system under the single-user mode from the commandline.
# poweroff -i -f
Alternatively, you may type Ctrl-Alt-Delete (The left-Ctrl-key, the left-Alt-Key, and the Delete are pressed together) to shutdown if "/etc/inittab" contains "ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -h now" in it.
See inittab(5) for details.
A text-mode full-screen file manager
A program to allow limited root privileges to users
Unix text editor Vi IMproved, a programmers text editor (standard version)
Unix text editor Vi IMproved, a programmers text editor (compact version)
GNU project Emacs, the Lisp based extensible text editor
Text-mode WWW browsers
The Unix style cut-and-paste on the text console (daemon)
It may be a good idea to read some informative documentations.
Debian Project documentation, (Debian FAQ) and other documents
Debian Policy Manual and related documents
Guidelines and information for Debian developers
Debian New Maintainers' Guide
History of the Debian Project
Debian FAQ
You can install some of these packages by the following.
# apt-get install package_name
system with the following.
(basic concept)
(survival method)
(basic method)
(shell mechanism)
(text processing method)
operating systems,
are organized into .
All files and directories are arranged in one big tree rooted at "/". It's called a tree because if you draw the filesystem, it looks like a tree but it is upside down.
These files and directories can be spread out over several devices. mount(8) serves to attach the filesystem found on some device to the big file tree.
Conversely, umount(8) detaches it again.
On recent Linux kernels, mount(8) with some options can bind part of a file tree somewhere else or can mount filesystem as shared, private, slave, or unbindable.
Supported mount options for each filesystem are available in "/usr/share/doc/linux-doc-*/Documentation/filesystems/".
Directories on Unix systems are called folders on some other systems.
Please also note that there is no concept for drive such as "A:" on any Unix system.
There is one filesystem, and everything is included. This is a huge advantage compared to Windows.
, , , , , and , where the path contains a device name such as "C:\".
(However, directory entries do exist that refer to physical devices as a part of the normal filesystem.
While you can use almost any letters or symbols in a file name, in practice it is a bad idea to do so.
It is better to avoid any characters that often have special meanings on the command line, including spaces, tabs, newlines, and other special characters: { } ( ) [ ] ' ` " \ / & & | ; ! # & ^ * % @ $ .
If you want to separate words in a name, good choices are the period, hyphen, and underscore.
You could also capitalize each word, "LikeThis". Experienced Linux users tend to avoid spaces in filenames.
The word "root" can mean either "root user" or "root directory".
The context of their usage should make it clear.
The word path is used not only for fully-qualified filename as above but also for the command search path.
The intended meaning is usually clear from the context.
The detailed best practices for the file hierarchy are described in the Filesystem Hierarchy Standard ("/usr/share/doc/debian-policy/fhs/fhs-2.3.txt.gz" and hier(7)).
You should remember the following facts as the starter.
under which physical data on hard disks and other storage devices reside, and the interaction with the hardware devices such as console screens and remote serial consoles are represented in an unified manner under "/dev/".
Each file, directory, named pipe (a way two programs can share data), or physical device on a Debian GNU/Linux system has a data structure called an
which describes its associated attributes such as the user who owns it (owner), the group that it belongs to, the time last accessed, etc.
The idea of representing just about everything in the filesystem was a Unix innovation, and modern Linux kernels have developed this idea ever further. Now, even information about processes running in the computer can be found in the filesystem.
This abstract and unified representation of physical entities and internal processes is very powerful since this allows us to use the same command for the same kind of operation on many totally different devices. It is even possible to change the way the kernel works by writing data to special files that are linked to running processes.
If you need to identify the correspondence between the file tree and the physical entity, execute mount(8) with no arguments.
system are defined for three categories of affected users.
The user who owns the file (u)
Other users in the group which the file belongs to (g)
All other users (o) also referred to as "world" and "everyone"
For the file, each corresponding permission allows following actions.
The read (r) permission allows owner to examine contents of the file.
The write (w) permission allows owner to modify the file.
The execute (x) permission allows owner to run the file as a command.
For the directory, each corresponding permission allows following actions.
The read (r) permission allows owner to list contents of the directory.
The write (w) permission allows owner to add or remove files in the directory.
The execute (x) permission allows owner to access files in the directory.
Here, the execute permission on a directory means not only to allow reading of files in that directory but also to allow viewing their attributes, such as the size and the modification time.
ls(1) is used to display permission information (and more) for files and directories.
When it is invoked with the "-l" option, it displays the following information in the order given.
Type of file (first character)
Access permission of the file (nine characters, consisting of three characters each for user, group, and other in this order)
Number of hard links to the file
Name of the user who owns the file
Name of the group which the file belongs to
Size of the file in characters (bytes)
Date and time of the file (mtime)
Name of the file
file creation scheme where all files created in the directory belong to the group of the directory.
Setting the sticky bit on a directory prevents a file in the directory from being removed by a user who is not the owner of the file.
In order to secure contents of a file in world-writable directories such as "/tmp" or in group-writable directories, one must not only reset the write permission for the file but also set the sticky bit on the directory.
Otherwise, the file can be removed and a new file can be created with the same name by any user who has write access to the directory.
Here are a few interesting examples of file permissions.
$ ls -l /etc/passwd /etc/shadow /dev/ppp /usr/sbin/exim4
crw------T 1 root root
108, 0 Oct 16 20:57 /dev/ppp
-rw-r--r-- 1 root root
2761 Aug 30 10:38 /etc/passwd
-rw-r----- 1 root shadow
1695 Aug 30 10:38 /etc/shadow
-rwsr-xr-x 1 root root
973824 Sep 23 20:04 /usr/sbin/exim4
$ ls -ld /tmp /var/tmp /usr/local /var/mail /usr/src
drwxrwxrwt 14 root root
20480 Oct 16 21:25 /tmp
drwxrwsr-x 10 root staff
4096 Sep 29 22:50 /usr/local
drwxr-xr-x 10 root root
4096 Oct 11 00:28 /usr/src
drwxrwsr-x
2 root mail
4096 Oct 15 21:40 /var/mail
drwxrwxrwt
3 root root
4096 Oct 16 21:20 /var/tmp
There is an alternative numeric mode to describe file permissions with chmod(1).
This numeric mode uses 3 to 4 digit wide octal (radix=8) numbers.
The hardware devices are just another kind of file on the Debian system.
If you have problems accessing devices such as CD-ROM and USB memory stick from a user account, you should make that user a member of the relevant group.
Some notable system-provided groups allow their members to access particular files and devices without root privilege.
Duplicate name for an existing file
"ln foo bar"
Special file that points to another file by name
"ln -s foo bar"
See the following example for changes in link counts and the subtle differences in the result of the rm command.
$ umask 002
$ echo "Original Content" & foo
$ ls -li foo
1449840 -rw-rw-r-- 1 penguin penguin 17 Oct 16 21:42 foo
$ ln foo bar
# hard link
$ ln -s foo baz
$ ls -li foo bar baz
1449840 -rw-rw-r-- 2 penguin penguin 17 Oct 16 21:42 bar
1450180 lrwxrwxrwx 1 penguin penguin
3 Oct 16 21:47 baz -& foo
1449840 -rw-rw-r-- 2 penguin penguin 17 Oct 16 21:42 foo
$ echo "New Content" & foo
$ ls -li foo bar baz
1449840 -rw-rw-r-- 1 penguin penguin 17 Oct 16 21:42 bar
1450180 lrwxrwxrwx 1 penguin penguin
3 Oct 16 21:47 baz -& foo
1450183 -rw-rw-r-- 1 penguin penguin 12 Oct 16 21:48 foo
Original Content
New Content
The hardlink can be made within the same filesystem and shares the same inode number which the "-i" option with ls(1)
The symlink always has nominal file access permissions of "rwxrwxrwx", as shown in the above example, with the effective access permissions dictated by permissions of the file that it points to.
It is generally a good idea not to create complicated symbolic links or hardlinks at all unless you have a very good reason.
It may cause nightmares where the logical combination of the symbolic links results in loops in the filesystem.
It is generally preferable to use symbolic links rather than hardlinks unless you have a good reason for using a hardlink.
directory links to the directory that it appears in, thus the link count of any new directory starts at 2.
directory links to the parent directory, thus the link count of the directory increases with the addition of new subdirectories.
If you are just moving to Linux from Windows, it soon becomes clear how well-designed the filename linking of Unix is, compared with the nearest Windows equivalent of "shortcuts".
Because it is implemented in the filesystem, applications can't see any difference between a linked file and the original. In the case of hardlinks, there really is no difference.
is a file that acts like a pipe.
You put something into the file, and it comes out the other end.
Thus it's called a FIFO, or First-In-First-Out: the first thing you put in the pipe is the first thing to come out the other end.
If you write to a named pipe, the process which is writing to the pipe doesn't terminate until the information being written is read from the pipe.
If you read from a named pipe, the reading process waits until there is nothing to read before terminating.
The size of the pipe is always zero --- it does not store data, it just links two processes like the functionality offered by the shell "|" syntax.
However, since this pipe has a name, the two processes don't have to be on the same command line or even be run by the same user. Pipes were a very influential innovation of Unix.
For example, try the following
$ mkfifo mypipe
$ echo "hello" &mypipe & # put into background
$ ls -l mypipe
prw-rw-r-- 1 penguin penguin 0 Oct 16 21:49 mypipe
$ cat mypipe
echo "hello" &mypipe
$ ls mypipe
$ rm mypipe
The exchange of information may occur over the network between different hosts.
The two most common ones are
"netstat -an" provides a very useful overview of sockets that are open on a given system.
refer to physical or virtual devices on your system, such as your hard disk, video card, screen, or keyboard.
An example of a virtual device is the console, represented by "/dev/console".
There are 2 types of device files.
Character device
Accessed one character at a time
1 character = 1 byte
E.g. keyboard device, serial port, …
Block device
accessed in larger units called blocks
1 block & 1 byte
E.g. hard disk, …
You can read and write device files, though the file may well contain binary data which may be an incomprehensible-to-humans gibberish.
Writing data directly to these files is sometimes useful for the troubleshooting of hardware connections.
For example, you can dump a text file to the printer device "/dev/lp0" or send modem commands to the appropriate serial port "/dev/ttyS0".
But, unless this is done carefully, it may cause a major disaster.
So be cautious.
For the normal access to a printer, use lp(1).
The device node number are displayed by executing ls(1) as the following.
$ ls -l /dev/sda /dev/sr0 /dev/ttyS0 /dev/zero
brw-rw---T
1 root disk
0 Oct 16 20:57 /dev/sda
brw-rw---T+ 1 root cdrom
0 Oct 16 21:53 /dev/sr0
crw-rw---T
1 root dialout
4, 64 Oct 16 20:57 /dev/ttyS0
crw-rw-rw-
1 root root
5 Oct 16 20:57 /dev/zero
"/dev/sda" has the major device number 8 and the minor device number 0.
This is read/write accessible by users belonging to the disk group.
"/dev/sr0" has the major device number 11 and the minor device number 0.
This is read/write accessible by users belonging to the cdrom group.
"/dev/ttyS0" has the major device number 4 and the minor device number 64.
This is read/write accessible by users belonging to the dialout group.
"/dev/zero" has the major device number 1 and the minor device number 5.
This is read/write accessible by anyone.
On the modern Linux system, the filesystem under "/dev/" is automatically populated by the udev(7) mechanism.
mounted on "/proc" and "/sys" are the pseudo-filesystem and expose internal data structures of the kernel to the userspace.
In other word, these entries are virtual, meaning that they act as a convenient window into the operation of the operating system.
The directory "/proc" contains (among other things) one subdirectory for each process running on the system, which is named after the process ID (PID). System utilities that access process information, such as ps(1), get their information from this directory structure.
The directories under "/proc/sys/" contain interfaces to change certain kernel parameters at run time.
(You may do the same through the specialized sysctl(8) command or its preload/configuration file "/etc/sysctl.conf".)
People frequently panic when they notice one file in particular - "/proc/kcore" - which is generally huge.
This is (more or less) a copy of the content of your computer's memory.
It's used to debug the kernel.
It is a virtual file that points to computer memory, so don't worry about its size.
The directory under "/sys" contains exported kernel data structures, their attributes, and their linkages between them. It also contains interfaces to change certain kernel parameters at run time.
See "proc.txt(.gz)", "sysfs.txt(.gz)" and other related documents in the Linux kernel documentation ("/usr/share/doc/linux-doc-*/Documentation/filesystems/*") provided by the linux-doc-* package.
is a temporary filesystem which keeps all files in the .
The data of the tmpfs in the
on memory may be swapped out to the
on disk as needed.
The directory "/run" is mounted as the tmpfs in the early boot process.
This enables writing to it even when the directory "/" is mounted as read-only.
This is the new location for the storage of transient state files and replaces several locations described in the
version 2.3:
"/var/run" → "/run"
"/var/lock" → "/run/lock"
"/dev/shm" → "/run/shm"
See "tmpfs.txt(.gz)" in the Linux kernel documentation ("/usr/share/doc/linux-doc-*/Documentation/filesystems/*") provided by the linux-doc-* package.
is a GNU "Swiss army knife" for the Linux console and other terminal environments.
This gives newbie a menu driven console experience which is much easier to learn than standard Unix commands.
You may need to install the Midnight Commander package which is titled "mc" by the following.
$ sudo apt-get install mc
Use the mc(1) command to explore the Debian system.
This is the best way to learn.
Please explore few interesting locations just using the cursor keys and Enter key.
"/etc" and its subdirectories
"/var/log" and its subdirectories
"/usr/share/doc" and its subdirectories
"/sbin" and "/bin"
This is a very convenient MC feature.
: the GNU Bourne Again SHell (de facto standard)
: an enhanced version of
Debian , good for shell script
: the standard shell with many enhancements
A version of the
C Shell, a version of
with builtin commands (Not meant for standard "/bin/sh")
the real, AT&T version of the
implementation of the
Policy-compliant Ordinary SHell (pdksh derivative)
Although POSIX-like shells share the basic syntax, they can differ
in behavior for things as basic as shell variables and glob expansions.
Please check their documentation for details.
In this tutorial chapter, the interactive shell always means bash.
The bash-completion package enables programmable completion for bash.
environment, there are few key strokes which have special meanings.
Please note that on a normal Linux character console, only the left-hand Ctrl and Alt keys work as expected.
Here are few notable key strokes to remember.
programs which are popular in the Unix-like system.
I think getting used to Vim commands is the right thing to do, since Vi-editor is always there in the Linux/Unix world.
(Actually, original vi or new nvi are programs you find everywhere.
I chose Vim instead for newbie since it offers you help through F1 key while it is similar enough and more powerful.)
If you chose either
instead as your choice of the editor, that is another good choice indeed, particularly for programming.
Emacs has a plethora of other features as well, including functioning as a newsreader, directory editor, mail program, etc.
When used for programming or editing shell scripts, it intelligently recognizes the format of what you are working on, and tries to provide assistance.
Some people maintain that the only program they need on Linux is Emacs.
Ten minutes learning Emacs now can save hours later.
Having the GNU Emacs manual for reference when learning Emacs is highly recommended.
All these programs usually come with tutoring program for you to learn them by practice.
Start Vim by typing "vim" and press F1-key.
You should at least read the first 35 lines.
Then do the online training course by moving cursor to "|tutor|" and pressing Ctrl-].
Good editors, such as Vim and Emacs, can handle UTF-8 and other exotic encoding texts correctly.
It is a good idea to use the X environment in the UTF-8 locale and to install required programs and fonts to it.
Editors have options to set the file encoding independent of the X environment.
Please refer to their documentation on multibyte text.
For the consistency on the Debian system, set these to "/usr/bin/editor". (Historically, "$EDITOR" was "ed" and "$VISUAL" was "vi".)
change the behavior of some Unix commands.
Default values of environment variables are initially set by the PAM system and then some of them may be reset by some application programs.
The display manager such as gdm3 resets environment variables.
The shell in its start up codes resets environment variables in "~/.bash_profile" and "~/.bashrc".
For language codes and country codes, see pertinent description in the "info gettext".
For the codeset on the modern Debian system, you should always set it to UTF-8 unless you specifically want to use the historic one with good reason and background knowledge.
For fine details of the locale configuration, see .
The "LANG=en_US" is not "LANG=C" nor "LANG=en_US.UTF-8". It is "LANG=en_US.ISO-8859-1" (see ).
value "en_US.UTF-8".
For the second command, "$LANG" is set to the French UTF-8
value "fr_FR.UTF-8".
Most command executions usually do not have preceding environment variable definition.
For the above example, you can alternatively execute as the following.
$ LANG=fr_FR.UTF-8
dimanche 3 juin :33 (UTC+0900)
As you can see here, the output of command is affected by the environment variable to produce French output.
If you want the environment variable to be inherited to subprocesses (e.g., when calling shell script), you need to export it instead by the following.
$ export LANG
When you use a typical console terminal, the "$LANG" environment variable is usually set to be exported by the desktop environment.
So the above is not really a good example to test the effect of export.
When filing a bug report, running and checking the command under "LANG=en_US.UTF-8" is a good idea if you use non-English environment.
See locale(5) and locale(7) for "$LANG" and related environment variables.
I recommend you to configure the system environment just by the "$LANG" variable and to stay away from "$LC_*" variables unless it is absolutely needed.
compliant date string.
BASH can be tweaked to change its glob behavior with its shopt builtin options such as "dotglob", "noglob", "nocaseglob", "nullglob", "extglob", etc.
See bash(1).
python(1) with the re module can do every conceivable text processing. See "/usr/share/doc/python/html/index.html".
If you are not sure what exactly these commands do, please use "man command" to figure it out by yourself.
Sort order and range expression are locale dependent.
If you wish to obtain traditional behavior for a command, use C locale instead of UTF-8 ones by prepending command with "LANG=C" (see
regular expressions (perlre(1)), , and
regular expressions offered by the re module have many common extensions to the normal ERE.
are used in many text processing tools.
They are analogous to the shell globs, but they are more complicated and powerful.
The regular expression describes the matching pattern and is made up of text characters and metacharacters.
A metacharacter is just a character with a special meaning.
There are 2 major styles, BRE and ERE, depending on the text tools as described above.
for the latest .
Awk is frequently used to extract data from these types of files.
For example, try the following
$ awk '{ print $3 }' &DPL
# month started
$ awk '($1=="Ian") { print }' &DPL
# DPL called Ian
January 1998
$ awk '($2=="Perens") { print $3,$4 }' &DPL # When Perens started
April 1996
Shells such as Bash can be also used to parse this kind of file.
For example, try the following
$ while read f do
echo $month
... same output as the first Awk example
Here, the read builtin command uses characters in "$IFS" (internal field separators) to split lines into words.
If you change "$IFS" to ":", you can parse "/etc/passwd" with shell nicely.
$ oldIFS="$IFS"
# save old value
$ while read user password uid gid rest_of_ do
if [ "$user" = "bozo" ]; then
echo "$user's ID is $uid"
done & /etc/passwd
bozo's ID is 1000
$ IFS="$oldIFS"
# restore old value
(If Awk is used to do the equivalent, use "FS=':'" to set the field separator.)
IFS is also used by the shell to split results of parameter expansion, command substitution, and arithmetic expansion.
These do not occur within double or single quoted words.
The default value of IFS is &space&, &tab&, and &newline& combined.
Be careful about using this shell IFS tricks.
Strange things may happen, when shell interprets some parts of the script as its input.
$ IFS=":,"
# use ":" and "," as IFS
$ echo IFS=$IFS,
IFS="$IFS"
# echo is a Bash builtin
# just a command output
Sat, 23 Aug :15 +0200
$ echo $(date -R)
# sub shell --& input to main shell
$ unset IFS
# reset IFS to the default
$ echo $(date -R)
Sat, 23 Aug :50 +0200
When using the shell interactive mode becomes too complicated, please consider to write a shell script (see ).