如下安装units包时，报错。

install.packages("units")

报错内容：

* installing *source* package ‘units’ ...
** package ‘units’ successfully unpacked and MD5 sums checked
** using staged installation
configure: units: 0.8-2
checking whether the C++ compiler works... yes
checking for C++ compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether the compiler supports GNU C++... yes
checking whether g++ -std=gnu++14 accepts -g... yes
checking for g++ -std=gnu++14 option to enable C++11 features... none needed
checking for stdio.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for strings.h... yes
checking for sys/stat.h... yes
checking for sys/types.h... yes
checking for unistd.h... yes
checking for _Bool... no
checking for stdbool.h that conforms to C99... yes
checking for error_at_line... yes
checking for gcc... gcc
checking whether the compiler supports GNU C... yes
checking whether gcc accepts -g... yes
checking for gcc option to enable C11 features... none needed
checking for XML_ParserCreate in -lexpat... yes
checking for udunits2.h... no
checking for udunits2/udunits2.h... no
checking for ut_read_xml in -ludunits2... no
configure: error: in `/tmp/RtmptLYHlx/R.INSTALLaf0c4dacedf9/units':
configure: error:
--------------------------------------------------------------------------------
  Configuration failed because libudunits2.so was not found. Try installing:
    * deb: libudunits2-dev (Debian, Ubuntu, ...)
    * rpm: udunits2-devel (Fedora, EPEL, ...)
    * brew: udunits (OSX)
  If udunits2 is already installed in a non-standard location, use:
    --configure-args='--with-udunits2-lib=/usr/local/lib'
  if the library was not found, and/or:
    --configure-args='--with-udunits2-include=/usr/include/udunits2'
  if the header was not found, replacing paths with appropriate values.
  You can alternatively set UDUNITS2_INCLUDE and UDUNITS2_LIBS manually.
--------------------------------------------------------------------------------

yum  install udunits2-devel

检查udunits2库路径是否正确设置。您可以在终端中执行以下命令，查找libudunits2.so的路径：

find / -name "libudunits2.so"

再次安装units包即可通过了。