Compression command
Common compressed file extensions
- . tar: Tar program packages files without compression
- .tar. GZ: Tar program package file, gzip compressed
- .tar. Bz2: Tar program package file, bzip2 compression
- .tar. xz: Tar program package file, compressed by xz
- . GZ: gzip program zip file
- . Z: compress program compresses files
- . bz2: bzip2 program zip file
- . XZ: XZ program zip file
- . zip: zip program zip file
As mentioned before, file extensions under linux are useless. Compressed files have multiple extensions to support a variety of compression commands. gzip, bz2, zip, etc. are commonly used. At present, compress is not commonly used. The purpose of tar packaging files is to integrate multiple files into a single file to facilitate compression with one command
gzip
Gzip is the most widely used compression command, which can unlock compressed files such as compress, zip, gzip, etc
gzip [-cdtv#] filename zcat filename.gz -c : Output compressed data to screen -d : decompression -t : Detect compressed file consistency(Are there any errors) -v : Display original file/Compression ratio of compressed file -# : #Refers to the number 1-9. 1 is the fastest and 9 has the highest compression ratio. The default is 6
The files compressed by gzip command can be decompressed by WinRAR and 7zip software under windows system
decompression
gzip -d filename.gz gupzip filename.gz
The zcat command can read the data of the compressed file and use the egrep command to find the keywords in the compressed file
In addition, the znew command is used to convert compress ed files to gzip format
bzip2
bz2 has a better compression ratio than gzip, and its usage is roughly the same, but when compressing large files, the compression time is significantly longer than gzip
bzip2 [-cdkzv#] filename bzcat filename.bz2 -c : Output compressed data to screen -d : decompression -k : Keep original file -z : Compression parameters -v : Display original file/Compression ratio of compressed file -# : #Refers to the number 1-9. 1 is the fastest and 9 has the highest compression ratio. The default is 6
xz
Bzip2 has a better compression ratio than gzip, and its usage is the same as the first two
xz [-dtlkc#] filename xcat filename.xz -d : decompression -t : Test compressed file integrity(Are there any errors) -l : Lists information about compressed files -k : Keep original file -c : Compressed data output to screen -# : #Refers to the number 1-9. 1 is the fastest and 9 has the highest compression ratio. The default is 6
Packaging command tar
Tar packages multiple directories and files into a large file, and compresses the files through the support of gzip, bzip2 and XZ At present, WinRAR under Windows is also supported tar.gz format file decompression
tar -[zjJ] [cv] [-f filename.tar] filename # pack tar -[zjJ] [tv] [-f filename.tar] # View file name tar -[zjJ] [xv] [-f filename.tar] [-C directory] # Extract to directory -c: Create package file -t: View the file names contained in the packaged file -x: decompression -z: Use after packing gzip compress -j: Use after packing bzip2 compress -J: Use after packing xz compress -v: The packaging process displays the file name processed -f filename: -f Followed by the file name to be processed -C: Followed by the extracted directory -p: Preserve the permissions and properties of backup data -P: Keep absolute path, Allow backup data to contain a root directory --exclude=FILE: Ignore files during packaging FILE
Examples of common commands
tar -jcv -f filename.tar.bz2 [filename|directory] # Packed and compressed with bzip2 tar -jtv -f filename.tar.bz2 # query tar -jxv -f filename.tar.bz2 -C directory # Unzip bzip2 to directory
CD recording technology
Although USB external hard disk is usually used to back up data, the CD-ROM is still available, which is worth discussing CD-ROM writing
- Create data as an iso file with the mkisofs command
- Burn to disc with cdrecord command
mkisofs
mkisofs [-o image] [-Jrv] [-V vol] [-m file] Files to be backed up > -graft-point isodir=systemdir -o: After image file name -J: Generate compatibility Windows File name structure, And allow names up to 64 in length unicode character -r: adopt Rock Ridge Generate support Unix/linux File data for -v: Show creation process -V vol: establish Volume -m file: Exclude files file -graft-point: Transplantation function
cdrecord
Since CentOS 7, the wodim command has been used for recording, but because it is compatible with the old version, cdrecord is still available. Wodim is linked to the cdrecord command
wodim --devices dev=/dev/sr0 # Query recorder bus location wodim -v dev=/dev/sr0 blank=[fast|all] # Erase repeat read / write disk wodim -v dev=/dev/sr0 -format # Format DVD+RW wodim -v dev=/dev/sr0 [-data|speed=X|-eject|fs=Ym] file.iso --devices: Scan the disk bus to find the recorder, Follow up equipment ATA Interface -v: Display process dev=/dev/sr0: Find the optical drive bus address blank=[fast|all]: Erase rewritable CD/DVD-RW, fast For fast, all For complete -format: format, But only for DVD+RW -data: Specify data format speed=X: Specify the recording speed -eject: Recording is complete. Eject the disc fs=Ym: The specified buffer size is Ym, The default is 4 m, Change according to actual parameters of recorder
Other compression / backup commands
dd
In addition to making files, dd is mainly used for backup
dd if="input_file" of="output_file" bs="block_size" count="number" if: Entered file/equipment of: Output file/equipment bs: set up block size, The default is 512 B(One sector) count: block Number of
cpio
cpio can back up any file, including the device
cpio -ovcB > [file|device] # backups cpio -ivcdu < [file|device] # reduction cpio -ivct < [file|device] # see
You need to use CPIO in combination with find to find files, such as backing up all files of / boot to / TMP / boot cpio
cd / find boot | cpio -ocvB > /tmp/boot.cpio
decompression
cd /tmp cpio -idvc < /tmp/boot.cpio