I am not able to install pytorch or torchvision using conda.
Below is the stacktrace:

$ conda install pytorch torchvision -c pytorch
Solving environment: done
## Package Plan ##
  environment location: /home/ubuntu/anaconda3
  added / updated specs: 
    - pytorch
    - torchvision
The following NEW packages will be INSTALLED:
    ninja:       1.8.2-py37h6bb024c_1                              
    pytorch:     0.4.1-py37_py36_py35_py27__9.0.176_7.1.2_2 pytorch
    torchvision: 0.2.1-py37_1                               pytorch
Proceed ([y]/n)? y
Preparing transaction: failed
# >>>>>>>>>>>>>>>>>>>>>> ERROR REPORT <<<<<<<<<<<<<<<<<<<<<<
    Traceback (most recent call last):
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/exceptions.py", line 819, in __call__
        return func(*args, **kwargs)
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/cli/main.py", line 78, in _main
        exit_code = do_call(args, p)
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/cli/conda_argparse.py", line 77, in do_call
        exit_code = getattr(module, func_name)(args, parser)
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/cli/main_install.py", line 11, in execute
        install(args, parser, 'install')
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/cli/install.py", line 253, in install
        handle_txn(unlink_link_transaction, prefix, args, newenv)
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/cli/install.py", line 282, in handle_txn
        unlink_link_transaction.execute()
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/core/link.py", line 223, in execute
        self.verify()
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/common/io.py", line 46, in decorated
        return f(*args, **kwds)
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/core/link.py", line 200, in verify
        self.prepare()
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/core/link.py", line 192, in prepare
        stp.remove_specs, stp.update_specs)
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/core/link.py", line 282, in _prepare
        mkdir_p(transaction_context['temp_dir'])
      File "/home/ubuntu/anaconda3/lib/python3.7/site-packages/conda/gateways/disk/__init__.py", line 60, in mkdir_p
        makedirs(path)
      File "/home/ubuntu/anaconda3/lib/python3.7/os.py", line 221, in makedirs
        mkdir(name, mode)
    PermissionError: [Errno 13] Permission denied: '/home/ubuntu/anaconda3/.condatmp'
`$ /home/ubuntu/anaconda3/bin/conda install pytorch torchvision -c pytorch`
  environment variables:
                 CIO_TEST=<not set>
        CONDA_DEFAULT_ENV=base
                CONDA_EXE=/home/ubuntu/anaconda3/bin/conda
             CONDA_PREFIX=/home/ubuntu/anaconda3
    CONDA_PROMPT_MODIFIER=
         CONDA_PYTHON_EXE=/home/ubuntu/anaconda3/bin/python
               CONDA_ROOT=/home/ubuntu/anaconda3
              CONDA_SHLVL=1
          LD_LIBRARY_PATH=/usr/local/cuda-9.0/lib64:
                     PATH=/usr/local/cuda-9.0/bin:/home/ubuntu/bin:/home/ubuntu/.local/bin:/home
                          /ubuntu/anaconda3/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bi
                          n:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
       REQUESTS_CA_BUNDLE=<not set>
            SSL_CERT_FILE=<not set>
     active environment : base
    active env location : /home/ubuntu/anaconda3
            shell level : 1
       user config file : /home/ubuntu/.condarc
 populated config files : 
          conda version : 4.5.11
    conda-build version : 3.15.1
         python version : 3.7.0.final.0
       base environment : /home/ubuntu/anaconda3  (read only)
           channel URLs : https://conda.anaconda.org/pytorch/linux-64
                          https://conda.anaconda.org/pytorch/noarch
                          https://repo.anaconda.com/pkgs/main/linux-64
                          https://repo.anaconda.com/pkgs/main/noarch
                          https://repo.anaconda.com/pkgs/free/linux-64
                          https://repo.anaconda.com/pkgs/free/noarch
                          https://repo.anaconda.com/pkgs/r/linux-64
                          https://repo.anaconda.com/pkgs/r/noarch
                          https://repo.anaconda.com/pkgs/pro/linux-64
                          https://repo.anaconda.com/pkgs/pro/noarch
          package cache : /home/ubuntu/anaconda3/pkgs
                          /home/ubuntu/.conda/pkgs
       envs directories : /home/ubuntu/.conda/envs
                          /home/ubuntu/anaconda3/envs
               platform : linux-64
             user-agent : conda/4.5.11 requests/2.19.1 CPython/3.7.0 Linux/4.15.0-36-generic ubuntu/16.04 glibc/2.23
                UID:GID : 1000:1000
             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?
[y/N]: 
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    $ conda config --set report_errors false
              
The sure proof way would be to

sudo /home/ubuntu/anaconda3/bin/conda install pytorch torchvision -c pytorch
But this is venturing in some pretty messy territory.
I’d suggest 2 alternative options,
The best way to do this is do a user installation of anaconda3

such that which conda returns $HOME/anaconda3/bin/conda
The other way is to do

conda create -n yourenvname python=x.x

and call

conda activate yourenvname

when you wish to use your environment
Both options will separate you completely from the anaconda in /home/ubuntu/anaconda3. Probably someone has been tempering with it. Best to restrict the management of environments away from others thereby preventing these sort of errors from happening