转载：https://blog.csdn.net/ristarjia/article/details/104030677
请去原文查看，以下主要是为了备份

问题

ubuntu18.04下nvidia-settings无法保存设置

解决方法

打开终端执行

切记使用终端运行，才能查看出错日志，不要从开始菜单里面点击
nvidia-settings

点击 Save to X Configuration File 提示 Unable to open X config file ‘/etc/X11/xorg.conf’ for writing

看终端输出

Package xorg-server was not found in the pkg-config search path.
Perhaps you should add the directory containing xorg-server.pc' to the PKG_CONFIG_PATH environment variable No package 'xorg-server' found Package xorg-server was not found in the pkg-config search path. Perhaps you should add the directory containing xorg-server.pc'
to the PKG_CONFIG_PATH environment variable
No package 'xorg-server' found
Error accessing /usr/share/screen-resolution-extra/nvidia-polkit: No such file or directory

ERROR: Unable to open X config file '/etc/X11/xorg.conf' for writing.

发现没有 /usr/share/screen-resolution-extra/nvidia-polkit 文件

1. 进入目录cd /usr/share/screen-resolution-extra && ls
2. 发现存在nvidia-polkit.py
3. 于是为其创建软链接，并赋予可执行权限

sudo ln -s nvidia-polkit.py nvidia-polkit
sudo chmod +x nvidia-polkit

此时，执行Save to X Configuration File，若终端输出

Package xorg-server was not found in the pkg-config search path.
Perhaps you should add the directory containing `xorg-server.pc'
to the PKG_CONFIG_PATH environment variable
No package 'xorg-server' found
Traceback (most recent call last):
  File "/usr/share/screen-resolution-extra/nvidia-polkit", line 20, in <module>
    import sys, dbus, logging, os, re
ImportError: No module named dbus

ERROR: Unable to open X config file '/etc/X11/xorg.conf' for writing.

可能是因为pyhon版本问题
切换系统默认python版本至python3

sudo update-alternatives --install /usr/bin/python python /usr/bin/python2 100
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 150
sudo update-alternatives --display python

可看到当前选择python3

python - auto mode
  link best version is /usr/bin/python3
  link currently points to /usr/bin/python3
  link python is /usr/bin/python
/usr/bin/python2 - priority 100
/usr/bin/python3 - priority 150

此时，Save to X Configuration File应执行成功

附录：nvidia-polkit.py 内容

#!/usr/bin/python
# -*- coding: utf-8 -*-
## Copyright (C) 2001-2008 Alberto Milone <albertomilone@alice.it>

## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.

## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.

## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


import sys, dbus, logging, os, re
import optparse

SERVICE_NAME   = 'com.ubuntu.ScreenResolution.Mechanism'
OBJECT_PATH    = '/'
INTERFACE_NAME = 'com.ubuntu.ScreenResolution.Mechanism'

# Usage:
# python /usr/share/screen-resolution-extra/nvidia-polkit.py --help
#

def get_xkit_service(widget=None):
    '''returns a dbus interface to the screenresolution mechanism'''
    service_object = dbus.SystemBus().get_object(SERVICE_NAME, OBJECT_PATH)
    service = dbus.Interface(service_object, INTERFACE_NAME)

    return service


def main(options):
    exit_code = 1
    
    conf = get_xkit_service()
    if not conf:
        # dbus_cant_connect
        logging.error("cannot connect to dbus service")
        sys.exit(1)
    
    if options.filename and options.backup_filename:
        logging.debug('making backup of /etc/X11/xorg.conf to %s and writing %s to /etc/X11/xorg.conf' \
        % (options.backup_filename, options.filename))
        exit_code = conf.backupAndWriteXorgConf([options.backup_filename, options.filename])
    elif options.filename and not options.backup_filename:
        logging.debug('writing %s to /etc/X11/xorg.conf' % options.filename)
        exit_code = conf.writeXorgConf(options.filename)
    elif not options.filename and options.backup_filename:
        logging.debug('making backup of /etc/X11/xorg.conf to %s' % options.backup_filename)
        exit_code = conf.backupXorgConf(options.backup_filename)
    elif not options.filename and not options.backup_filename:
        logging.error("called with wrong arguments")
        return exit_code

    # All went well if exit_code == 0
    return exit_code


if __name__ == "__main__":
    parser = optparse.OptionParser()
    parser.add_option("-w", "--write-from", dest="filename",
                      help="write xorg.conf from FILE", metavar="FILE")
    parser.add_option("-b", "--backup-to", dest="backup_filename",
                      help="backup file to FILE", metavar="FILE")

    (options, args) = parser.parse_args()
    
    operation_status = main(options)

    sys.exit(operation_status)