一：卸载的时候出现的错误：
umount /dev/nb1
device is busy
解决：找到是什么进程使得他busy，用 lsof /dev/nb1 . kill掉那个进程,然后重新umount即可。
二：GD2编译的时候出现的错误：
The usual way to define `LIBTOOL’ is to add `AC_PROG_LIBTOOL’
Libtool library used but `LIBTOOL’ is undefined
[Makefile.in] Error 1
解决：缺少编译安装的软件包。如：yum install automake,libjpeg-devel,libpng-devel,freetype-devel,libtiff-devel,autoconf,gettext-devel,libtool
三：安装 snmp的时候出现的错误：
1>/bin/sed: can’t read /usr/lib/libbeecrypt.la: No such file or directory
libtool: link: `/usr/lib/libbeecrypt.la’ is not a valid libtool archive
make[1]: *** [libnetsnmpmibs.la] Error 1
解决：以为缺少libbeecrypt.la ，libbeecrypt.so等共享库，如：yum install libbeecrypt.la
2>/usr/bin/ld: cannot find -lelf
解决：ln -s /usr/lib/libelf.so.1 /usr/lib/libelf.so
3>/usr/bin/ld:can’t not find -lselinux
解决：缺少libselinux 和 libselinux-devel包，如：yum install libselinux
四：Rsync同步常见问题：
错误一：
@ERROR: auth failed on module xxxxx
rsync: connection unexpectedly closed (90 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(150)
解决：这是因为密码设置错了，无法登入成功，检查一下rsync.pwd，看客服是否匹配。还有服务器端没启动rsync 服务也会出现这种情况。
错误二：
password file must not be other-accessible
continuing without password file
Password:
解决：这是因为rsyncd.pwd rsyncd.sec的权限不对，应该设置为600。如：chmod 600 rsyncd.pwd
错误三：
@ERROR: chroot failed
rsync: connection unexpectedly closed (75 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(150)
解决：这是因为你在 rsync.conf 中设置的 path 路径不存在，要新建目录才能开启同步。
错误四：
rsync: failed to connect to 218.107.243.2: No route to host (113)
rsync error: error in socket IO (code 10) at clientserver.c(104) [receiver=2.6.9]
解决：对方没开机、防火墙阻挡、通过的网络上有防火墙阻挡，都有可能。关闭防火墙，其实就是把tcp udp 的873端口打开。
五：软件安装的时候常出现的问题：
configure: error: …No recognized SSL/TLS toolkit detected
# yum -y install openssl-devel
configure: error: no acceptable cc found in $PATH
yum -y install gcc-c++
configure: error: cannot find output from lex; giving up flex is not installed, install flex.
yum -y install flex
configure: error: xml2-config not found. Please check your libxml2 installation.
yum -y install libxml2-devel
configure: error: Cannot find OpenSSL’s
yum -y install openssl-devel
configure: error: Please reinstall the BZip2 distribution
yum -y install bzip2-devel
configure: error: Please reinstall the libcurl distribution - easy.h should be in /include/curl/
yum -y install curl-devel
configure: error: libjpeg.(a|so) not found.
yum -y install libjpeg-devel
configure: error: libpng.(a|so) not found.
yum -y install libpng-devel
configure: error: freetype2 not found!
yum -y install freetype-devel
configure: error: Unable to locate gmp.h
yum -y install gmp-devel
configure: error: Cannot find pspell
yum -y install aspell-devel
libtool: link: cannot find the library `/usr/lib/libbeecrypt.la’ (librpmio.la: /usr/lib/libbeecrypt.la)
解决：缺少beecrypt包，如：
http://sourceforge.net/projects/beecrypt下载beecrypt-4.1.2.tar.gz
然后运行如下命令：
#tar -zxvf beecrypt-4.1.2.tar.gz
#./configure
#make
#make install