Linux系统上安装软件最痛苦的事情莫过于配置过程，这其中etc文件的各种修改、各种备份、各种还原，有时候真是想死啊。
好吧，etckeeper就是用来解救etc修改和备份的。
本质上，etckeeper是基于版本系统进行管理的，但为什么不直接使用版本系统（如Git）进行备份管理呢？
实际上也可以直接用版本系统来管理/etc文件夹的，但是etckeeper在版本管理系统基础上针对/etc的使用场景进行了改进。
主要有以下几点（版本系统以git为例）：
1.etckeeper和git都可以进行文件系统的版本管理，但是etckeeper还保存了文件的元数据，如mode和group信息等
2.git和mercurial不能跟踪空文件夹，但是/etc下存在部分重要的空文件夹需要跟踪管理
3.etckeeper在安装和升级软件包前后可以自动提交/etc文件夹改动的内容
4.etckeeper可以每天进行备份提交
以下是etckeeper在Ubuntu 14.04.5上的安装和使用介绍。
1.etckeeper的安装
1.1.安装git
最常见的是etckeeper内部使用git进行版本管理，所以需要先安装git
ygu@ubuntu:~$ sudo apt-get install git-core
1.2.安装etckeepr
ygu@ubuntu:~$ sudo apt-get install etckeeper
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
etckeeper
0 upgraded, 1 newly installed, 0 to remove and 248 not upgraded.
Need to get 26.7 kB of archives.
After this operation, 216 kB of additional disk space will be used.
Get:1 http://mirrors.aliyun.com/ubuntu/ trusty/main etckeeper all 1.9ubuntu2 [26.7 kB]
Fetched 26.7 kB in 0s (58.6 kB/s)
Preconfiguring packages ...
Selecting previously unselected package etckeeper.
(Reading database ... 178087 files and directories currently installed.)
Preparing to unpack .../etckeeper_1.9ubuntu2_all.deb ...
Unpacking etckeeper (1.9ubuntu2) ...
Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
Setting up etckeeper (1.9ubuntu2) ...
etckeeper init not ran as bzr is not installed
etckeepr安装消息的最后一步提示说，由于bzr没有安装，所以没有运行etckeeper init进行初始化。
2.etckeeper的配置
2.1.配置文件路径
默认情况下，配置文件etckeeper.conf位于/etc/etckeeper文件夹内：
ygu@ubuntu:~$ cd /etc/etckeeper
ygu@ubuntu:/etc/etckeeper$ ls -lh
total 44K
drwxr-xr-x 2 root root 4.0K May 12 14:44 commit.d
-rw-r--r-- 1 root root 1.2K Feb 23 2014 etckeeper.conf
drwxr-xr-x 2 root root 4.0K May 12 14:44 init.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 list-installed.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 post-install.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 pre-commit.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 pre-install.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 unclean.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 uninit.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 update-ignore.d
drwxr-xr-x 2 root root 4.0K May 12 14:44 vcs.d
2.2.配置文件内容
安装好etckeeper后默认的配置内容如下：
ygu@ubuntu:/etc/etckeeper$ cat etckeeper.conf
# The VCS to use.
#VCS="hg"
#VCS="git"
VCS="bzr"
#VCS="darcs"
# Options passed to git commit when run by etckeeper.
GIT_COMMIT_OPTIONS=""
# Options passed to hg commit when run by etckeeper.
HG_COMMIT_OPTIONS=""
# Options passed to bzr commit when run by etckeeper.
BZR_COMMIT_OPTIONS=""
# Options passed to darcs record when run by etckeeper.
DARCS_COMMIT_OPTIONS="-a"
# Uncomment to avoid etckeeper committing existing changes
# to /etc automatically once per day.
#AVOID_DAILY_AUTOCOMMITS=1
# Uncomment the following to avoid special file warning
# (the option is enabled automatically by cronjob regardless).
#AVOID_SPECIAL_FILE_WARNING=1
# Uncomment to avoid etckeeper committing existing changes to
# /etc before installation. It will cancel the installation,
# so you can commit the changes by hand.
#AVOID_COMMIT_BEFORE_INSTALL=1
# The high-level package manager that's being used.
# (apt, pacman-g2, yum, zypper etc)
HIGHLEVEL_PACKAGE_MANAGER=apt
# The low-level package manager that's being used.
# (dpkg, rpm, pacman, pacman-g2, etc)
LOWLEVEL_PACKAGE_MANAGER=dpkg
# To push each commit to a remote, put the name of the remote here.
# (eg, "origin" for git).
PUSH_REMOTE=""
根据需要对etckeepr.conf进行修改，常见的改动有两项（包括用git进行管理和取消每天自动提交）：
1].使用git进行版本管理
将
#VCS="git"
VCS="bzr"
修改为：
VCS="git"
#VCS="bzr"
2].根据需要决定是否每天进行备份提交
如果不进行每天备份提交，将
#AVOID_DAILY_AUTOCOMMITS=1
修改为：
AVOID_DAILY_AUTOCOMMITS=1
etckeeper的设置选项意思很浅显，也带有很清楚的注释，其它选项可以根据实际需要进行修改。
3.etckeeper的使用
3.1.初始化
配置完etckeeper后的第一件事就是初始化。
ygu@ubuntu:/etc/etckeeper$ sudo etckeeper init
Initialized empty Git repository in /etc/.git/
如果不希望使用原来保存的历史，可以通过etckeeper uninit命令销毁历史记录。
ygu@ubuntu:/etc$ sudo etckeeper uninit
** Warning: This will DESTROY all recorded history for /etc,
** including the git repository.
Are you sure you want to do this? [yN] y
Proceeding..
如果安装etckeeper时已经使用bzr版本管理进行过初始化，则配置git管理时需要先etckeeper uninit再进行etckeeper init操作。
3.2.提交修改
初始化完后，进行提交。
ygu@ubuntu:/etc$ sudo etckeeper commit "initial commit"
每次对/etc改动后也使用etckeeper commit来提交。
etckeeper安装配置好后，日常维护只需要会这一个etckeeper commit操作就够了，简单不？
3.3.版本和分支管理
etckeeper没有提供单独的取消修改和分支创建切换的命令，这些操作都是通过git来进行，例如创建和切换分支，撤销和回溯版本等。
但是通过git更新文件后需要运行etckeeper init来更新文件属性。
例如，使用git切换到backup分支：
ygu@ubuntu:/etc$ sudo git checkout backup
ygu@ubuntu:/etc$ sudo etckeeper init
3.4.远程备份
/etc文件夹的内容，可以通过git推送到远程仓库实现备份，具体步骤如下：
# ssh登录guyongqiangx在目录/opt/etc-backup下创建远程库
# ssh 登录
ygu@ubuntu:/etc$ ssh ygu@guyongqiangx
ygu@guyongqiangx:~$ mkdir -p /opt/etc-backup
ygu@guyongqiangx:~$ cd /opt/etc-backup/
ygu@guyongqiangx:/opt/etc-backup$ chmod 700 .
# 创建版本库
ygu@guyongqiangx:/opt/etc-backup$ git init --bare
Initialized empty Git repository in /opt/etc-backup/
#
# 以上操作也可以通过一条ssh命令来完成：
# ssh ygu@guyongqiangx 'mkdir -p /opt/etc-backup; cd /opt/etc-backup; chmod 700 .; git init --bare'
#
# 本地注册guyongqiangx服务器的远程库
# 注册远程库
ygu@ubuntu:/etc$ sudo git remote add backup ssh://ygu@guyongqiangx/opt/etc-backup
# 显示远程库信息
ygu@ubuntu:/etc$ sudo git remote -v
backup ssh://ygu@guyongqiangx/opt/etc-backup (fetch)
backup ssh://ygu@guyongqiangx/opt/etc-backup (push)
# 将/etc内容推送到guyongqiangx的远程库
# 推送到远程库
ygu@ubuntu:/etc$ sudo git push backup --all
# 输入远程服务器登录密码
ygu@guyongqiangx's password:
Counting objects: 2488, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (1912/1912), done.
Writing objects: 100% (2488/2488), 1.73 MiB | 1.13 MiB/s, done.
Total 2488 (delta 341), reused 0 (delta 0)
To ssh://ygu@guyongqiangx/opt/etc-backup
* [new branch] master -> master
如果etckeeper有将数据备份到远程，最重要是要确保数据安全，例如，上面步骤中命令chmod 700 .将远程库的目录设置为只读。
将远程目录设置为700模式远远不够，因为备份的/etc目录下包含shadow文件，一旦远程备份目录被读取，所有/etc下的重要数据都泄露了。
4.废话太多，简单总结
以上内容比较多，最常见的操作有以下四个：
# 安装
$ apt-get install git-core etckeeper
# 修改配置文件，VCS="git"，AVOID_DAILY_AUTOCOMMITS=1
$ vi /etc/etckeeper/etckeeper.conf
# 初始化并第1次提交
$ etckeeper init
$ etckeeper commit "initial commit"
# 修改文件/etc/xxx并提交
$ vi /etc/xxx
$ etckeeper commit "commit message"
好吧，日常维护就只有etckeeper commit一条指令。