tar-compression

Archiving and compression

Overview

Skills for tar/gzip/xz archive compression and split-volume backup.

tar basics

Create an archive

# 创建 tar 归档
tar -cvf archive.tar /path/to/dir

# 创建并 gzip 压缩
tar -czvf archive.tar.gz /path/to/dir

# 创建并 bzip2 压缩
tar -cjvf archive.tar.bz2 /path/to/dir

Create and compress with xz

tar -cJvf archive.tar.xz /path/to/dir

Multiple directories/files

tar -czvf archive.tar.gz dir1 dir2 file1.txt

### 解压归档
```bash
# 解压 tar
tar -xvf archive.tar

# 解压 gzip
tar -xzvf archive.tar.gz

# 解压 bzip2
tar -xjvf archive.tar.bz2

# 解压 xz
tar -xJvf archive.tar.xz

# 解压到指定目录
tar -xzvf archive.tar.gz -C /target/dir

View contents

# 列出内容
tar -tvf archive.tar
tar -tzvf archive.tar.gz

# 搜索文件
tar -tzvf archive.tar.gz | grep "filename"

Common options

# 排除文件/目录
tar -czvf archive.tar.gz --exclude='*.log' --exclude='cache' /path

# 从文件读取排除列表
tar -czvf archive.tar.gz --exclude-from=exclude.txt /path

# 保留权限
tar -czvf archive.tar.gz --preserve-permissions /path

# 增量备份
tar -czvf archive.tar.gz --newer='2024-01-01' /path

Compression tools

gzip

# 压缩
gzip file.txt              # 生成 file.txt.gz，删除原文件
gzip -k file.txt           # 保留原文件
gzip -9 file.txt           # 最高压缩率

# 解压
gunzip file.txt.gz
gzip -d file.txt.gz

# 查看压缩文件
zcat file.txt.gz
zless file.txt.gz
zgrep "pattern" file.txt.gz

bzip2

# 压缩
bzip2 file.txt
bzip2 -k file.txt          # 保留原文件
bzip2 -9 file.txt          # 最高压缩率

# 解压
bunzip2 file.txt.bz2
bzip2 -d file.txt.bz2

# 查看
bzcat file.txt.bz2

xz

# 压缩
xz file.txt
xz -k file.txt             # 保留原文件
xz -9 file.txt             # 最高压缩率
xz -T 4 file.txt           # 多线程

# 解压
unxz file.txt.xz
xz -d file.txt.xz

# 查看
xzcat file.txt.xz

zstd

# 压缩
zstd file.txt
zstd -19 file.txt          # 最高压缩率
zstd -T0 file.txt          # 自动多线程

# 解压
unzstd file.txt.zst
zstd -d file.txt.zst

Split-volume backup

split splitting

# 按大小分割
split -b 100M archive.tar.gz archive.tar.gz.part_

# 按行分割
split -l 10000 largefile.txt part_

# 合并
cat archive.tar.gz.part_* > archive.tar.gz

tar split volumes

# 创建分卷
tar -czvf - /path/to/dir | split -b 100M - backup.tar.gz.part_

# 解压分卷
cat backup.tar.gz.part_* | tar -xzvf -

Common scenarios

Scenario 1: Website backup

#!/bin/bash
DATE=$(date +%Y%m%d)
BACKUP_DIR="/backup"
WEB_DIR="/var/www/html"

# 创建备份
tar -czvf ${BACKUP_DIR}/web_${DATE}.tar.gz \
    --exclude='*.log' \
    --exclude='cache/*' \
    ${WEB_DIR}

# 保留最近 7 天
find ${BACKUP_DIR} -name "web_*.tar.gz" -mtime +7 -delete

Scenario 2: Database backup compression

# MySQL
mysqldump -u root -p database | gzip > db_backup.sql.gz

# 解压恢复
gunzip < db_backup.sql.gz | mysql -u root -p database

# PostgreSQL
pg_dump database | xz > db_backup.sql.xz

Scenario 3: Incremental backup

#!/bin/bash
SNAPSHOT="/backup/snapshot.snar"
BACKUP_DIR="/backup"
SOURCE="/data"

# 完整备份（首次）
tar -czvf ${BACKUP_DIR}/full.tar.gz -g ${SNAPSHOT} ${SOURCE}

# 增量备份
tar -czvf ${BACKUP_DIR}/incr_$(date +%Y%m%d).tar.gz -g ${SNAPSHOT} ${SOURCE}

Scenario 4: Remote backup

# 本地压缩后传输
tar -czvf - /path/to/dir | ssh user@remote "cat > /backup/archive.tar.gz"

# 远程压缩
ssh user@remote "tar -czvf - /path/to/dir" > local_backup.tar.gz

Compression comparison

Format	Compression ratio	Speed	Memory	Use case
gzip	Medium	Fast	Low	Daily backup
bzip2	High	Slow	Medium	Archival storage
xz	Highest	Slowest	High	Long-term storage
zstd	High	Fast	Medium	Modern backup

Troubleshooting

Issue	Troubleshooting method
Decompression fails	Check file integrity and format
Insufficient space	Use pipes or split volumes
Lost permissions	Use --preserve-permissions
Corrupted file	Use gzip -t to test

# 测试压缩文件
gzip -t file.gz
bzip2 -t file.bz2
xz -t file.xz

# 修复损坏的 gzip
gzrecover file.gz

# 查看压缩信息
gzip -l file.gz