用PAX做差異備份

用PAX做差異備份

在windows的平台要設計出完整的備份方式要花不少錢買備份軟體才能做到,在非windows的平台上只要認真找一下,透過些指令就可以做到了

pax的一些基本用法：

用pax遞迴複製目錄

pax –rwv –pe /home /root

/root目錄要是已存在的

後為複製到哪個目錄
前面為要複製的資料目錄

把/home完整搬一份到/root下

用PAX做備份檔

pax -wvf /mnt/nfs/test/jackson.pax /home/jackson

察看備份檔內容

pax -vf /mnt/nfs/test/jackson.pax |more

還原備份檔

pax -rv -pe -f /mnt/nfs/test/jackson.pax

加上-i參數則為互動式還原

加上-pe為保留原檔案擁有者等屬性

還原時須注意：會將備份檔內的資料還原至原來的路徑下

例如：jackson.pas原本是從/home/Jackson備份而來的

就會還原回/home/Jackson，而覆蓋掉原來的檔案

所以若希望檔案不要直接被覆蓋，需先將原路徑的檔案做搬移或更名

完整備份範例

對/home目錄做成一個備份檔：/backup/home.pax

pax -wvf /backup/home.pax /home

增量備份範例

對/home目錄中，今天時間8:00之後有異動的資料做備份，

檔名為：/backup/home-diff.pax

Pax –wv –T 800 –f /backup/home-diff.pax /home

-T 參數使用：

-T [from_date][,to_date][/[c][m]]

Allow files to be
selected based on a file modification or inode change

time falling within a
specified time range of from_date to to_date (the

dates are inclusive).
If only a
from_date is supplied, all files with a

modification or inode
change time equal to or younger are selected.
If

only
a to_date is supplied, all files with a
modification or inode

change time equal to
or older will be selected. When the
from_date is

equal to the to_date,
only files with a modification or inode change

time of exactly that
time will be selected.

When pax is in the
write or copy mode, the optional trailing field

[c][m]
can be used to determine which file time (inode change,
file mod-

ification
or both) are used in the comparison. If neither is specified,

the
default is to use file modification time only.
The m specifies the

comparison of file
modification time (the time when the file was last

written). The c
specifies the comparison of inode change time (the time

when the file inode
was last changed; e.g., a change of owner, group,

mode, etc). When c
and m are both specified, then the modification and

inode change times are
both compared. The inode change time comparison

is useful in selecting
files whose attributes were recently changed or

selecting files which
were recently created and had their modification

time reset to an older
time (as what happens when a file is extracted

from an archive and
the modification time is preserved). Time compar-

isons using both file
times is useful when pax is used to create a time

based incremental
archive (only files that were changed during a speci-

fied time range will
be archived).

A
time range is made up of six different fields and each field must
con-

tain two digits. The
format is:

[[[[[cc]yy]mm]dd]HH]MM[.SS]

Where cc is the first
two digits of the year (the century), yy is the

last two digits of the
year, the first mm is the month (from 01 to 12),

dd is the day of the
month (from 01 to 31), HH is the hour of the day

(from 00 to 23), MM is
the minute (from 00 to 59), and SS is the seconds

(from 00 to 59). The
minute field MM is required, while the other

fields are optional
and must be added in the following order:

HH, dd, mm, yy,
cc.

The SS field may be
added independently of the other fields. Time

ranges are relative to
the current time, so

-T 1234/cm

would select all files
with a modification or inode change time of 12:34

PM today or later.
Multiple -T time range can be supplied and checking

stops with the first
match.

增量備份檔的說明

假設有個目錄/home/account做完整備份建立了account.pax
大小為100MB

當24小時候，其大小改變為150MB

則新的備份檔
account.pas才會產生，內容即為此150MB大小的資料

若經24小時做差異備份時，其大小未改變仍為100MB

則此次差異備份不對此檔案作備份

crontab的設定：

週1的0:00 做一次完整備份

週2到週日0:00做一次24小時的增量備份

以一個禮拜為循環

預計設定當做完完整備份時，把增量備份檔刪除

用以清出磁碟空間。