我的系统（Ubuntu Lucid）上安装了 2 个不同版本的 PostgreSQL：
- /var/lib/postgresql/8.4
- /var/lib/postgresql/9.0
默认情况下，当我运行诸如 createdb 或 psql 之类的 PostgreSQL 命令时，使用的是 9.0 版本。
如何将我的系统配置为默认使用 8.4 版本？
我正在遵循Nagios Ubuntu 快速入门说明。我在 Ubuntu 10.10 上并安装 Nagios 3.2.3。
在文档的底部，它说我需要安装 mailx 和 postfix 包。（已经安装了 Postfix。）但是当我尝试安装 mailx 时，我被问到要安装 3 个软件包中的哪一个：
$ sudo apt-get install mailx
[sudo] password for nagios:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package mailx is a virtual package provided by:
mailutils 1:2.1+dfsg1-4ubuntu1
heirloom-mailx 12.4-1.1
bsd-mailx 8.1.2-0.20090911cvs-2ubuntu1
You should explicitly select one to install.
E: Package mailx has no installation candidate
我应该安装哪一个？
在尝试安装 Nagios 3.2.3 时，我运行了他们的 ./configure 脚本并得到了这些错误：
checking for main in -liconv... no
checking for gdImagePng in -lgd (order 1)... no
checking for gdImagePng in -lgd (order 2)... no
checking for gdImagePng in -lgd (order 3)... no
checking for gdImagePng in -lgd (order 4)... no
*** GD, PNG, and/or JPEG libraries could not be located... *********
Boutell's GD library is required to compile the statusmap, trends
and histogram CGIs. Get it from http://www.boutell.com/gd/, compile
it, and use the --with-gd-lib and --with-gd-inc arguments to specify
the locations of the GD library and include files.
NOTE: In addition to the gd-devel library, you'll also need to make
sure you have the png-devel and jpeg-devel libraries installed
on your system.
NOTE: After you install the necessary libraries on your system:
1. Make sure /etc/ld.so.conf has an entry for the directory in
which the GD, PNG, and JPEG libraries are installed.
2. Run 'ldconfig' to update the run-time linker options.
3. Run 'make clean' in the Nagios distribution to clean out
any old references to your previous compile.
4. Rerun the configure script.
NOTE: If you can't get the configure script to recognize the GD libs
on your system, get over it and move on to other things. The
CGIs that use the GD libs are just a small part of the entire
Nagios package. Get everything else working first and then
revisit the problem. Make sure to check the nagios-users
mailing list archives for possible solutions to GD library
problems when you resume your troubleshooting.
********************************************************************
我要哪个包？libgd2-xpm-dev？libgd2-noxpm-dev？php5-gd？我不想自己做任何图像处理——我只是想让 Nagios 工作。
我想在创建新用户时在每个新用户的主目录中自动创建一个名为“.virtualenvs”的目录。
我正在使用 useradd 命令来创建新用户。
我希望从现在开始的每个新用户都默认使用 bash 作为他们的 shell。
我知道要将自己的 shell 更改为 bash，您将使用命令“chsh -s /bin/bash”，但是如何将所有未来用户的 shell 默认自动设置为 bash？
我想做类似的事情
$ play filename.mid
无需打开图形程序即可听到 MIDI 文件的播放。是否有适用于 Ubuntu 的软件包可以做到这一点？
在/etc/sudoers我看到这个：
# Allow members of group sudo to execute any command after they have
# provided their password
# (Note that later entries override this, so you might need to move
# it further down)
%sudo ALL=(ALL) ALL
那么如何将用户添加到该sudo组？