Linux, Use dd command to backup system

Backup:
# dd if=/dev/hdx bs=1M conv=sync,noerror | gzip > /path/to/image.gz

Hdx could be hda, hdb etc. In the second example gzip is used to compress the image if it is really just a backup.

Restore:
# gzip -dc /path/to/image.gz | dd of=/dev/hdx bs=1M conv=sync,noerror

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將映像檔依照檔案大小作分割

# dd if=/dev/hdx bs=4k conv=sync,noerror | gzip -c | split -b 2000m - /path/to/backup.img.gz

The - option tells split to read from stdin. Otherwise, split would interpret the /mnt/hdc1... as the file to be split.

# cat /mnt/hdx/backup.img.gz.* | gzip -dc | dd of=/dev/hda1 bs=4k conv=sync,noerror

Bash - sdiff, compare two file

# sdiff -s file1 file2

< 代表file1有file2沒有
> 代表file1沒有file2有
|  代表file1有file2有，但是不相同

其他參數

-w 30 限定輸出字元30個
-s 只顯示不同的行

Ref. http://note.tc.edu.tw/943.html

CentOS - Upgrade kernel

Option 1.
# rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm (external link)
# yum install --enablerepo=elrepo-kernel install kernel-ml
# yum remove kernel-{firmware,headers,devel}
# yum install --enablerepo=elrepo-kernel kernel-ml-{firmware,headers,devel}

Option 2. Recommend
http://www.thegeekstuff.com/2013/06/compile-linux-kernel/
You can ignore “make menuconfig” (which may require extra libs) by using current
kernel config file like this:
change folder to kernel src folder
# cp /boot/config-3.10.0 .config
# make olddefconfig
# make
# make modules
# make modules_install
# make install

Bash - Date format

依測試時間用來建立test log folder...
# date --date="now" +"%Y%m%d-%H-%M-%S"