当我尝试在ubuntu20.04上运行GAMIT下的doy命令时，显示：

root@DESKTOP-LF0EAC9:/etc/apt# doy
doy: error while loading shared libraries: libgfortran.so.3: cannot open shared object file: No such file or directory

其中libgfortran.so.3依赖于gfortran-6，则尝试安装gfortran-6：

root@DESKTOP:/etc/apt# apt install gfortran-6
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package gfortran-6

这里的问题是ubuntu20.04不支持g+±6，添加以下源至/etc/apt/sources.list，添加源方式见链接

deb http://gb.archive.ubuntu.com/ubuntu/ bionic main universe

运行

sudo apt-get update

安装gcc++ -6

apt-get install g++-6

设置gcc默认版本

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-6 6

安装gfortran-6

 apt install gfortran-6

安装成功，运行doy

root@DESKTOP-LF0EAC9:/etc/apt# doy 2020 001
Date 2020/01/01  0:00 hrs, DOY   1 JD  2458849.5000 MJD  58849.0000
GPS Week  2086 Day of week  3, GPS Seconds 259200 Day of Week Wed
Decimal Year 2020.000000000 GRACE Seconds 631108800.0

运行成功