check_compiler_abi_compatibility(compiler)
      File "/home/multiai3/anaconda3/envs/oamil/lib/python3.7/site-packages/torch/utils/cpp_extension.py", line 294, in check_compiler_abi_compatibility
        if not check_compiler_ok_for_platform(compiler):
      File "/home/multiai3/anaconda3/envs/oamil/lib/python3.7/site-packages/torch/utils/cpp_extension.py", line 254, in check_compiler_ok_for_platform
        which = subprocess.check_output(['which', compiler], stderr=subprocess.STDOUT)
      File "/home/multiai3/anaconda3/envs/oamil/lib/python3.7/subprocess.py", line 411, in check_output
        **kwargs).stdout
      File "/home/multiai3/anaconda3/envs/oamil/lib/python3.7/subprocess.py", line 512, in run
        output=stdout, stderr=stderr)
    subprocess.CalledProcessError: Command '['which', 'g++']' returned non-zero exit status 1.
    [end of output]

note: This error originates from a subprocess, and is likely not a problem with pip.

安装mmcv报错note: This error originates from a subprocess, and is likely not a problem with pip

竟然是因为没有C++编辑器。我重装系统后没有安装。所以之前能编译的，重装后不能编译。

计算机环境真是玄学。

apt-get install gcc

apt-get install gcc

安装后问题解决。