莫名奇妙出现这个问题：

# >>>>>>>>>>>>>>>>>>>>>> ERROR REPORT <<<<<<<<<<<<<<<<<<<<<<

    Traceback (most recent call last):
      File "/root/anaconda3/lib/python3.7/site-packages/conda/exceptions.py", line 1079, in __call__
        return func(*args, **kwargs)
      File "/root/anaconda3/lib/python3.7/site-packages/conda/cli/main.py", line 84, in _main
        exit_code = do_call(args, p)
      File "/root/anaconda3/lib/python3.7/site-packages/conda/cli/conda_argparse.py", line 82, in do_call
        return getattr(module, func_name)(args, parser)
      File "/root/anaconda3/lib/python3.7/site-packages/conda/cli/main_update.py", line 20, in execute
        install(args, parser, 'update')
      File "/root/anaconda3/lib/python3.7/site-packages/conda/cli/install.py", line 116, in install
        if context.use_only_tar_bz2:
      File "/root/anaconda3/lib/python3.7/site-packages/conda/base/context.py", line 710, in use_only_tar_bz2
        import conda_package_handling.api
      File "/root/anaconda3/lib/python3.7/site-packages/conda_package_handling/api.py", line 140, in <module>
        tmpdir_root=_tempfile.gettempdir(), processes=None):
      File "/root/anaconda3/lib/python3.7/tempfile.py", line 294, in gettempdir
        tempdir = _get_default_tempdir()
      File "/root/anaconda3/lib/python3.7/tempfile.py", line 229, in _get_default_tempdir
        dirlist)
    FileNotFoundError: [Errno 2] No usable temporary directory found in ['/tmp', '/var/tmp', '/usr/tmp', '/']

`$ /root/anaconda3/bin/conda update -n base -c defaults conda`

  environment variables:
                 CIO_TEST=<not set>
        CONDA_DEFAULT_ENV=FairMOT
                CONDA_EXE=/root/anaconda3/bin/conda
             CONDA_PREFIX=/root/anaconda3/envs/FairMOT
           CONDA_PREFIX_1=/root/anaconda3
    CONDA_PROMPT_MODIFIER=(FairMOT)
         CONDA_PYTHON_EXE=/root/anaconda3/bin/python
               CONDA_ROOT=/root/anaconda3
              CONDA_SHLVL=2
          LD_LIBRARY_PATH=/usr/local/nvidia/lib:/usr/local/nvidia/lib64
             LIBRARY_PATH=/usr/local/cuda/lib64/stubs
                     PATH=/root/anaconda3/bin:/root/anaconda3/envs/FairMOT/bin:/root/anaconda3/c
                          ondabin:/usr/local/nvidia/bin:/usr/local/cuda/bin:/usr/local/sbin:/usr
                          /local/bin:/usr/sbin:/usr/bin:/sbin:/bin
       REQUESTS_CA_BUNDLE=<not set>
            SSL_CERT_FILE=<not set>

     active environment : FairMOT
    active env location : /root/anaconda3/envs/FairMOT
            shell level : 2
       user config file : /root/.condarc
 populated config files : /root/.condarc
          conda version : 4.8.3
    conda-build version : 3.18.8
         python version : 3.7.3.final.0
       virtual packages : __cuda=10.2
                          __glibc=2.23
       base environment : /root/anaconda3  (writable)
           channel URLs : https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/linux-64
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/noarch
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/free/linux-64
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/free/noarch
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/r/linux-64
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/r/noarch
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/pro/linux-64
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/pro/noarch
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/msys2/linux-64
                          https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/msys2/noarch
          package cache : /root/anaconda3/pkgs
                          /root/.conda/pkgs
       envs directories : /root/anaconda3/envs
                          /root/.conda/envs
               platform : linux-64
             user-agent : conda/4.8.3 requests/2.22.0 CPython/3.7.3 Linux/3.10.0-957.el7.x86_64 ubuntu/16.04.6 glibc/2.23
                UID:GID : 0:0
             netrc file : None
           offline mode : False


An unexpected error has occurred. Conda has prepared the above report.

If submitted, this report will be used by core maintainers to improve
future releases of conda.
Would you like conda to send this report to the core maintainers?

LZ的解决方法：

conda clean -i

然后就可以了。。。也不知道具体是啥问题，但就是解决了