WINDOWS COMMAND
WINDOWS COMMAND
This section gives insight into the most important
commands of your SuSE Linux system. Along with the individual commands,
parameters are listed and, where appropriate, a typical sample application is
introduced. To learn more about the various commands, it is usually possible to
get additional information with the man program followed by the name
of the command, for example, man ls.
In these manual pages, move up and down with PgUp and PgDn and
move between the beginning and the end of a document with Home and End.
End this viewing mode by pressing Q. Learn more about the man command
itself with man.
There are many more commands than listed in this
chapter. For information about other commands or more detailed information, we
recommend the O'Reilly publication Linux in a Nutshell. In the following
overview, the individual command elements are written in different typefaces.
The actual command is always printed as command.
Without this, nothing can function.
Options without which the respective program cannot
function are printed in italics.
Further details, like file names, which must be
passed to a command for correct functioning, are written in
the Courier font.
Specifications or parameters that are not required
are placed in [brackets].
Adjust possible specifications to your needs. It
makes no sense to write ls file(s), if no file named file(s) actually
exists. You can usually combine several parameters, for example, by
writing ls -la instead of ls -l -a.
ls [option(s)] [file(s)]
If
you run ls without any additional parameters, the program will list
the contents of the current directory in short form.
-l
detailed list
-a
displays hidden files
cp [option(s)] sourcefile targetfile
-i
Waits for confirmation, if necessary, before an
existing targetfile is overwritten
-r
Copies recursively (includes subdirectories)
mv [option(s)] sourcefile targetfile
-b
Creates a backup copy of the sourcefile before
moving
-i
Waits for confirmation, if necessary, before an
existing targetfile is overwritten
rm [option(s)] file(s)
Removes the specified files from the file system.
Directories are not removed by rm unless the option -r is
used.
-r
Deletes any existing subdirectories
-i
Waits for confirmation before deleting each file.
ln [option(s)] sourcefile targetfile
Creates
an internal link from the sourcefile to
the targetfile, under a different name. Normally, such a link points
directly to the sourcefile on one and the same file system. However,
if ln is executed with the -s option, it creates a symbolic
link that only points to the directory where the sourcefile is
located, thus enabling linking across file systems.
-s
Creates a symbolic link
cd [options(s)] [directory]
mkdir [option(s)] directoryname
rmdir [option(s)] directoryname
chown [option(s)] username.group file(s)
-R
Changes files and directories in all subdirectories.
chgrp [option(s)] groupname file(s)
Transfers
the group ownership of a given file to the group with the specified
group name. The file owner can only change group ownership if a member of both
the existing and the new group.
chmod [options] mode file(s)
The mode parameter has three parts: group, access,
and access type. group accepts the following characters:
u
user
g
group
o
others
For access, access is granted by the + symbol
and denied by the - symbol.
The access type is controlled by the
following options:
r
read
w
write
x
eXecute — executing files or changing to the
directory.
s
Set uid bit — the application or program is started
as if it were started by the owner of the file.
gzip [parameters] file(s)
This program compresses the contents of files, using
complex mathematical algorithms. Files compressed in this way are given the
extension .gz and need to be uncompressed before they can be used. To
compress several files or even entire directories, use the tar command.
-d
decompresses the packed gzip files so they return to
their original size and can be processed normally (like the command gunzip).
tar options archive file(s)
tar is a quite complex command with a number of
options available. The most frequently used options are:
-f
Writes the output to a file and not to the screen as
is usually the case
-c
Creates a new tar archive
-r
Adds files to an existing archive
-t
Outputs the contents of an archive
-u
Adds files, but only if they are newer than the
files already contained in the archive
-x
Unpacks files from an archive (extraction)
-z
Packs the resulting archive with gzip
-j
Compresses the resulting archive with bzip2
-v
Lists files processed
The archive files created by tar end
with .tar. If the tar archive was also compressed using gzip, the
ending is .tgz or .tar.gz. If it was compressed using bzip2, .tar.bz2.
Application examples can be found in Section “Archives and Data Compression”.
locate pattern(s)
The locate command can find in which
directory a specified file is located. If desired, use wild cards to
specify file names. The program is very speedy, as it uses a database
specifically created for the purpose (rather than searching through the entire
file system). This very fact, however, also results in a major
drawback: locate is unable to find any files created after the latest
update of its database.
The database can be generated by root with updatedb.
updatedb [options(s)]
This
command performs an update of the database used by locate. To include
files in all existing directories, run the program as root. It also makes
sense to place it in the background by appending an ampersand (&), so you
can immediately continue working on the same command line (updatedb &).
find [option(s)]
The find command allows you to search for
a file in a given directory. The first argument specifies the directory in
which to start the search. The option -name must be followed by a
search string, which may also include wild cards. Unlike locate, which uses a
database, find scans the actual directory.
The cat command
displays the contents of a file, printing the entire contents to the screen
without interruption.
-n
Numbers the output on the left margin
less [option(s)] file(s)
This
command can be used to browse the contents of the specified file. Scroll half a
screen page up or down with PgUp and PgDn or a full screen
page down with Space. Jump to the beginning or end of a file using Home and End.
Press Q to exit the program.
grep [option(s)] searchstring filenames
The grep command finds a specific searchstring in
the specified file(s). If the search string is found, the command displays
the line in which the searchstring was found along with the file
name.
-i
Ignores case
-l
Only displays the names of the respective files, but
not the text lines
-n
Additionally displays the numbers of the lines in
which it found a hit
-l
Only lists the files in
which searchstring does not occur
diff [option(s)] file1 file2
The diff command compares the contents of
any two files. The output produced by the program lists all lines that do not
match.
This is frequently used by programmers who need only
send their program alterations and not the entire source code.
-q
Only reports whether the two given files differ
This command can be used to mount any data media,
such as hard disks, CD-ROM drives, and other drives, to a directory of the
Linux file system.
-r
mount read-only
-t filesystem
Specifies the file system. The most common are ext2 for
Linux hard disks, msdos for MS-DOS media, vfat for the
Windows file system, and iso9660 for CDs.
For hard disks not
defined in the file /etc/fstab, the device type must also be specified. In
this case, only root can mount. If the file system should also be
mounted by other users, enter the option userin the appropriate line in
the /etc/fstab file (separated by commas) and save this change.
Further information is available in mount.
This command unmounts a mounted drive from the file
system. To prevent data loss, run this command before taking a removable data
medium from its drive. Normally, only root is allowed to run the
commands mount and umount. To enable other users to run these
commands, edit the /etc/fstab file to specify the option user for
the respective drive.
The df (disk
free) command, when used without any options, displays information about the
total disk space, the disk space currently in use, and the free space on all
the mounted drives. If a directory is specified, the information is limited to
the drive on which that directory is located.
-H
shows the number of occupied blocks in gigabytes,
megabytes, or kilobytes — in human-readable format
-t
Type of file system (ext2, nfs, etc.)
du [option(s)] [path]
This
command, when executed without any parameters, shows the total disk space
occupied by files and subdirectories in the current directory.
-a
Displays the size of each individual file
-h
Output in human-readable form
-s
Displays only the calculated total size
free [option(s)]
The
command free displays information about RAM and swap space usage,
showing the total and the used amount in both categories.
-b
Output in bytes
-k
Output in kilobytes
-m
Output in megabytes
date [option(s)]
This
simple program displays the current system time. If run as root, it can
also be used to change the system time. Details about the program are available
in date.
top provides
a quick overview of the currently running processes. Press H to access a page
that briefly explains the main options to customize the program.
ps [option(s)] [process ID]
If run without any options, this command displays a
table of all your own programs
or processes — those you started. The options for this command
are not preceded by hyphen.
Displays a detailed list of all processes,
independent of the owner.
kill [option(s)] process ID
Unfortunately, sometimes a program cannot be
terminated in the normal way. However, in most cases, you should still be able
to stop such a runaway program by executing the kill command,
specifying the respective process ID (see top and ps).
kill sends a TERM signal that instructs the program to shut itself down.
If this does not help, the following parameter can be used:
-9
Sends a KILL signal
instead of a TERM signal,
with which the process really is annihilated by
the operating system. This brings the specific processes to an end in almost
all cases.
killall [option(s)] processname
This
command is similar to kill, but uses the process name (instead of the
process ID) as an argument, causing all processes with that name to be killed.
ping [option(s)] host name|IP address
The ping command
is the standard tool for testing the basic functionality of TCP/IP networks. It
sends a small data packet to the destination host, requesting an immediate
reply. If this works, pingdisplays a message to that effect, which indicates
that the network link is basically functioning.
-c
number Determines the total number of packages
to send and ends after they have been dispatched. By default, there is no
limitation set.
-f
flood ping:
sends as many data packages as possible. A popular means, reserved to root,
to test networks.
-i
value Specifies the interval between two data
packages in seconds. Default: one second
nslookup
The
Domain Name System resolves domain names to IP addresses. With this tool, send
queries to information servers (DNS servers).
telnet [option(s)] host name or IP address
Telnet is actually an Internet protocol that enables
you to work on remote hosts across a network. telnet is also the name
of a Linux program that uses this protocol to enable operations on remote
computers.
passwd [option(s)] [username]
Users may change their own passwords at any time
using this command. Furthermore, the administrator root can use the
command to change the password of any user on the system.
su [option(s)] [username]
The su command
makes it possible to log in under a different user name from a running session.
When using the command without specifying a user name, you will be prompted for
the root password. Specify a user name and the corresponding password
to use the environment of the respective user. The password is not required
from root, as root is authorized to assume
the identity of any user.
halt [option(s)]
To avoid loss of data, you should always use this
program to shut down your system.
clear
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