LPI Linux Certification in a Nutshell (16 page)

bzip2

bzip2 [
options
] [
filenames ...
]
bunzip2 [
options
] [
filenames ...
]

Compress or
uncompress files using the
Burrows-Wheeler block sorting text compression
algorithm
and
Huffman coding.
bzip2
is
generally considered one of the most efficient compression
programs available for Linux systems. Files compressed with
bzip2
usually have the
extension
.bz2
.

Compress the file
/etc/largefile
using the highest level
of compression. It will be compressed and renamed
/etc/largefile.bz2
:

$
bzip2 -9 /etc/largefile

Uncompress
/etc/largefile.bz2
. It will be
uncompressed and renamed
/etc/largefile
:

$
bunzip2 /etc/largefile.bz2

or:

$
bzip2 -d /etc/largefile.bz2

cp

cp [
options
]
file1 file2
cp [
options
]
files directory

In the first command form, copy
file1
to
file2
. If
file2
exists and you have appropriate
privileges, it will be overwritten without warning (unless you use
the
-i
option). Both
file1
and
file2
can be any valid filename, either
fully qualified or in the local directory. In the second command
form, copy
files
to
directory
. Note that the presence of
multiple files implies that you wish to copy the files to a
directory. If
directory
doesn’t exist,
an error message will be printed. This command form can get you in
trouble if you attempt to copy a single file into a directory that
doesn’t exist, as the command will be interpreted as the first
form and you’ll end up with
file2
instead of
directory
.

Copy the messages file to the local directory (specified by
.
):

$
cp /var/log/messages .

Make an identical copy, including preservation of file
attributes, of directory
src
in new
directory
src2
:

$
cp -Rp src src2

Copy
file1, file2, file5, file6
,
and
file7
from the local directory into
your home directory (in
bash
):

$
cp file1 file2 file[567] ~

cpio

cpio –o [
options
] < [
filenames ...
] > [archive]
cpio –i < [archive]
cpio –p [destination-directory] < [filenames...]

cpio
is used to
create and extract archives, or copy files from one
place to another. No
compression
is done natively on
these archives; you must employ
gzip
or
bzip2
if you desire
compression
.

Create an archive that contains all the files in the current
working directory:

$
ls | cpio –ov > /tmp/archive.cpio

Notice that instead of passing files to archive to
cpio
on the command line, we had the
ls
command create a list of files for us,
which we then send to the
cpio
command via
standard input using the
|
(vertical bar) character.

Extract all the files from the archive we just
created:

$
cpio –iv < /tmp/archive.cpio

dd

dd [
options
]

dd
converts and copies files.
It is one of the few commands in the Linux world that can operate
directly on
block devices, rather than requiring access through
the filesystem layer. This is especially useful when performing
backups of block devices, such as hard drive partitions, CD-ROMs,
or floppy disks.

Create an image of the compact disc currently in the default
CD drive (
/dev/cdrom
):

$
dd if=/dev/cdrom of=/tmp/cd.img

Copy
/tmp/file
to
/tmp/file2
, converting all
characters to lowercase:

$
dd if=/tmp/file of=/tmp/file2 conv=lcase

file

file [
options
] [
file
]

file
is designed to determine
the kind of file being queried. Because Linux (and other Unix-like
systems) don’t require filename extensions to determine the type
of a file, the
file
command is useful when
you’re unsure what kind of file you’re dealing with.
file
accomplishes this by performing three
sets of tests on the file in question: filesystem tests, magic
tests, and language tests.
Filesystem tests involved examining the output of
the
“stat” system call.
Magic tests are used to check for files with data in
particular fixed formats. If neither of these tests results in a
conclusive answer, a
language test is performed to determine whether the
file is some sort of text file.

Determine the file type of the currently running
kernel:

$
file /boot/vmlinuz-2.6.27.29-170.2.78.fc10.i686
/boot/vmlinuz-2.6.27.29-170.2.78.fc10.i686: Linux kernel x86 boot executable \
RO-rootFS, root_
0x902, swap_dev 0x2, Normal VGA

Determine the file type of
/etc/passwd
:

$
file /etc/passwd
/etc/passwd: ASCII text

find

find [
options
] [
path...
] [
expression
]

find
searches
recursively through directory trees for files or directories that
match certain
characteristics
.
find
can then either print the file or
directory that matches or perform other operations on the
matches.

Find all files in
/tmp
that end in
.c
and print them
to standard out:

$
find /tmp –name "*.c"

The expression
"*.c"
means “all files that end in .c”. This is an example of
file globbing
and is explained
in detail later in this Objective.

Find files (and only files) in
/tmp
older than seven days. Do not
recurse into subdirectories of
/tmp
:

$
find /tmp -maxdepth 1 -type f -daystart -ctime +7

Find files in
/usr
that
have the
setuid
permission bit
set (mode 4000):

$
find /usr -perm -4000

gzip and gunzip

gzip [
options
] [
filenames ...
]
gunzip [
options
] [
filenames ...
]

Compress or
uncompress files using Lempel-Ziv coding.
gzip
is one of the most common compression
formats found on Linux systems, although it is starting to be
replaced by the more efficient
bzip2
. Files
compressed with
gzip
usually
have the extension
.gz
.
Command-line options for
gzip
are very
similar to those for
bzip2
.

Compress the file
/etc/largefile
. It will be compressed
and renamed
/etc/largefile.gz
:

$
gzip /etc/largefile

Uncompress
/etc/largefile.gz
. It will be
uncompressed and renamed
/etc/largefile
:

$
gunzip /etc/largefile.gz

or:

$
gzip -d /etc/largefile.gz