1. The system is centos7.4, installation apache2.4.6. I forgot to back up the configuration file at first, and then modified the configuration file, resulting in failed at startup. The following is a detailed error log.

2.80

1. selimun

4. Finally, the configured httpd.config

-sharp
-sharp This is the main Apache HTTP server configuration file.  It contains the
-sharp configuration directives that give the server its instructions.
-sharp See <URL:http://httpd.apache.org/docs/2.4/> for detailed information.
-sharp In particular, see 
-sharp <URL:http://httpd.apache.org/docs/2.4/mod/directives.html>
-sharp for a discussion of each configuration directive.
-sharp
-sharp Do NOT simply read the instructions in here without understanding
-sharp what they do.  They"re here only as hints or reminders.  If you are unsure
-sharp consult the online docs. You have been warned.  
-sharp
-sharp Configuration and logfile names: If the filenames you specify for many
-sharp of the server"s control files begin with "/" (or "drive:/" for Win32), the
-sharp server will use that explicit path.  If the filenames do *not* begin
-sharp with "/", the value of ServerRoot is prepended -- so "log/access_log"
-sharp with ServerRoot set to "/www" will be interpreted by the
-sharp server as "/www/log/access_log", where as "/log/access_log" will be
-sharp interpreted as "/log/access_log".

-sharp
-sharp ServerRoot: The top of the directory tree under which the server"s
-sharp configuration, error, and log files are kept.
-sharp
-sharp Do not add a slash at the end of the directory path.  If you point
-sharp ServerRoot at a non-local disk, be sure to specify a local disk on the
-sharp Mutex directive, if file-based mutexes are used.  If you wish to share the
-sharp same ServerRoot for multiple httpd daemons, you will need to change at
-sharp least PidFile.
-sharp
ServerRoot "/etc/httpd"

-sharp
-sharp Listen: Allows you to bind Apache to specific IP addresses and/or
-sharp ports, instead of the default. See also the <VirtualHost>
-sharp directive.
-sharp
-sharp Change this to Listen on specific IP addresses as shown below to 
-sharp prevent Apache from glomming onto all bound IP addresses.
-sharp
-sharpListen 12.34.56.78:80
Listen 80

-sharp
-sharp Dynamic Shared Object (DSO) Support
-sharp
-sharp To be able to use the functionality of a module which was built as a DSO you
-sharp have to place corresponding `LoadModule" lines at this location so the
-sharp directives contained in it are actually available _before_ they are used.
-sharp Statically compiled modules (those listed by `httpd -l") do not need
-sharp to be loaded here.
-sharp
-sharp Example:
-sharp LoadModule foo_module modules/mod_foo.so
-sharp
Include conf.modules.d/*.conf

-sharp
-sharp If you wish httpd to run as a different user or group, you must run
-sharp httpd as root initially and it will switch.  
-sharp
-sharp User/Group: The name (or -sharpnumber) of the user/group to run httpd as.
-sharp It is usually good practice to create a dedicated user and group for
-sharp running httpd, as with most system services.
-sharp
User apache
Group apache

-sharp "Main" server configuration
-sharp
-sharp The directives in this section set up the values used by the "main"
-sharp server, which responds to any requests that aren"t handled by a
-sharp <VirtualHost> definition.  These values also provide defaults for
-sharp any <VirtualHost> containers you may define later in the file.
-sharp
-sharp All of these directives may appear inside <VirtualHost> containers,
-sharp in which case these default settings will be overridden for the
-sharp virtual host being defined.
-sharp

-sharp
-sharp ServerAdmin: Your address, where problems with the server should be
-sharp e-mailed.  This address appears on some server-generated pages, such
-sharp as error documents.  e.g. admin@your-domain.com
-sharp
ServerAdmin root@localhost

-sharp
-sharp ServerName gives the name and port that the server uses to identify itself.
-sharp This can often be determined automatically, but we recommend you specify
-sharp it explicitly to prevent problems during startup.
-sharp
-sharp If your host doesn"t have a registered DNS name, enter its IP address here.
-sharp
-sharpServerName www.example.com:80
ServerName localhost:80

-sharp
-sharp Deny access to the entirety of your server"s filesystem. You must
-sharp explicitly permit access to web content directories in other 
-sharp <Directory> blocks below.
-sharp
<Directory />
    AllowOverride none
    Require all denied
</Directory>

-sharp
-sharp Note that from this point forward you must specifically allow
-sharp particular features to be enabled - so if something"s not working as
-sharp you might expect, make sure that you have specifically enabled it
-sharp below.
-sharp

-sharp
-sharp DocumentRoot: The directory out of which you will serve your
-sharp documents. By default, all requests are taken from this directory, but
-sharp symbolic links and aliases may be used to point to other locations.
-sharp
DocumentRoot "/var/www/html"

-sharp
-sharp Relax access to content within /var/www.
-sharp
<Directory "/var/www">
    AllowOverride None
    -sharp Allow open access:
    Require all granted
</Directory>

-sharp Further relax access to the default document root:
<Directory "/var/www/html">
    -sharp
    -sharp Possible values for the Options directive are "None", "All",
    -sharp or any combination of:
    -sharp   Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews
    -sharp
    -sharp Note that "MultiViews" must be named *explicitly* --- "Options All"
    -sharp doesn"t give it to you.
    -sharp
    -sharp The Options directive is both complicated and important.  Please see
    -sharp http://httpd.apache.org/docs/2.4/mod/core.html-sharpoptions
    -sharp for more information.
    -sharp
    Options Indexes FollowSymLinks

    -sharp
    -sharp AllowOverride controls what directives may be placed in .htaccess files.
    -sharp It can be "All", "None", or any combination of the keywords:
    -sharp   Options FileInfo AuthConfig Limit
    -sharp
    AllowOverride None

    -sharp
    -sharp Controls who can get stuff from this server.
    -sharp
    Require all granted
</Directory>

-sharp
-sharp DirectoryIndex: sets the file that Apache will serve if a directory
-sharp is requested.
-sharp
<IfModule dir_module>
    DirectoryIndex index.html
</IfModule>

-sharp
-sharp The following lines prevent .htaccess and .htpasswd files from being 
-sharp viewed by Web clients. 
-sharp
<Files ".ht*">
    Require all denied
</Files>

-sharp
-sharp ErrorLog: The location of the error log file.
-sharp If you do not specify an ErrorLog directive within a <VirtualHost>
-sharp container, error messages relating to that virtual host will be
-sharp logged here.  If you *do* define an error logfile for a <VirtualHost>
-sharp container, that host"s errors will be logged there and not here.
-sharp
ErrorLog "logs/error_log"

-sharp
-sharp LogLevel: Control the number of messages logged to the error_log.
-sharp Possible values include: debug, info, notice, warn, error, crit,
-sharp alert, emerg.
-sharp
LogLevel warn

<IfModule log_config_module>
    -sharp
    -sharp The following directives define some format nicknames for use with
    -sharp a CustomLog directive (see below).
    -sharp
    LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined
    LogFormat "%h %l %u %t \"%r\" %>s %b" common

    <IfModule logio_module>
      -sharp You need to enable mod_logio.c to use %I and %O
      LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" %I %O" combinedio
    </IfModule>

    -sharp
    -sharp The location and format of the access logfile (Common Logfile Format).
    -sharp If you do not define any access logfiles within a <VirtualHost>
    -sharp container, they will be logged here.  Contrariwise, if you *do*
    -sharp define per-<VirtualHost> access logfiles, transactions will be
    -sharp logged therein and *not* in this file.
    -sharp
    -sharpCustomLog "logs/access_log" common

    -sharp
    -sharp If you prefer a logfile with access, agent, and referer information
    -sharp (Combined Logfile Format) you can use the following directive.
    -sharp
    CustomLog "logs/access_log" combined
</IfModule>

<IfModule alias_module>
    -sharp
    -sharp Redirect: Allows you to tell clients about documents that used to 
    -sharp exist in your server"s namespace, but do not anymore. The client 
    -sharp will make a new request for the document at its new location.
    -sharp Example:
    -sharp Redirect permanent /foo http://www.example.com/bar

    -sharp
    -sharp Alias: Maps web paths into filesystem paths and is used to
    -sharp access content that does not live under the DocumentRoot.
    -sharp Example:
    -sharp Alias /webpath /full/filesystem/path
    -sharp
    -sharp If you include a trailing / on /webpath then the server will
    -sharp require it to be present in the URL.  You will also likely
    -sharp need to provide a <Directory> section to allow access to
    -sharp the filesystem path.

    -sharp
    -sharp ScriptAlias: This controls which directories contain server scripts. 
    -sharp ScriptAliases are essentially the same as Aliases, except that
    -sharp documents in the target directory are treated as applications and
    -sharp run by the server when requested rather than as documents sent to the
    -sharp client.  The same rules about trailing "/" apply to ScriptAlias
    -sharp directives as to Alias.
    -sharp
    ScriptAlias /cgi-bin/ "/var/www/cgi-bin/"

</IfModule>

-sharp
-sharp "/var/www/cgi-bin" should be changed to whatever your ScriptAliased
-sharp CGI directory exists, if you have that configured.
-sharp
<Directory "/var/www/cgi-bin">
    AllowOverride None
    Options None
    Require all granted
</Directory>

<IfModule mime_module>
    -sharp
    -sharp TypesConfig points to the file containing the list of mappings from
    -sharp filename extension to MIME-type.
    -sharp
    TypesConfig /etc/mime.types

    -sharp
    -sharp AddType allows you to add to or override the MIME configuration
    -sharp file specified in TypesConfig for specific file types.
    -sharp
    -sharpAddType application/x-gzip .tgz
    -sharp
    -sharp AddEncoding allows you to have certain browsers uncompress
    -sharp information on the fly. Note: Not all browsers support this.
    -sharp
    -sharpAddEncoding x-compress .Z
    -sharpAddEncoding x-gzip .gz .tgz
    -sharp
    -sharp If the AddEncoding directives above are commented-out, then you
    -sharp probably should define those extensions to indicate media types:
    -sharp
    AddType application/x-compress .Z
    AddType application/x-gzip .gz .tgz

    -sharp
    -sharp AddHandler allows you to map certain file extensions to "handlers":
    -sharp actions unrelated to filetype. These can be either built into the server
    -sharp or added with the Action directive (see below)
    -sharp
    -sharp To use CGI scripts outside of ScriptAliased directories:
    -sharp (You will also need to add "ExecCGI" to the "Options" directive.)
    -sharp
    -sharpAddHandler cgi-script .cgi

    -sharp For type maps (negotiated resources):
    -sharpAddHandler type-map var

    -sharp
    -sharp Filters allow you to process content before it is sent to the client.
    -sharp
    -sharp To parse .shtml files for server-side includes (SSI):
    -sharp (You will also need to add "Includes" to the "Options" directive.)
    -sharp
    AddType text/html .shtml
    AddOutputFilter INCLUDES .shtml
</IfModule>

-sharp
-sharp Specify a default charset for all content served; this enables
-sharp interpretation of all content as UTF-8 by default.  To use the 
-sharp default browser choice (ISO-8859-1), or to allow the META tags
-sharp in HTML content to override this choice, comment out this
-sharp directive:
-sharp
AddDefaultCharset UTF-8

<IfModule mime_magic_module>
    -sharp
    -sharp The mod_mime_magic module allows the server to use various hints from the
    -sharp contents of the file itself to determine its type.  The MIMEMagicFile
    -sharp directive tells the module where the hint definitions are located.
    -sharp
    MIMEMagicFile conf/magic
</IfModule>

-sharp
-sharp Customizable error responses come in three flavors:
-sharp 1) plain text 2) local redirects 3) external redirects
-sharp
-sharp Some examples:
-sharpErrorDocument 500 "The server made a boo boo."
-sharpErrorDocument 404 /missing.html
-sharpErrorDocument 404 "/cgi-bin/missing_handler.pl"
-sharpErrorDocument 402 http://www.example.com/subscription_info.html
-sharp

-sharp
-sharp EnableMMAP and EnableSendfile: On systems that support it, 
-sharp memory-mapping or the sendfile syscall may be used to deliver
-sharp files.  This usually improves server performance, but must
-sharp be turned off when serving from networked-mounted 
-sharp filesystems or if support for these functions is otherwise
-sharp broken on your system.
-sharp Defaults if commented: EnableMMAP On, EnableSendfile Off
-sharp
-sharpEnableMMAP off
EnableSendfile on

-sharp Supplemental configuration
-sharp
-sharp Load config files in the "/etc/httpd/conf.d" directory, if any.
IncludeOptional conf.d/*.conf

problem description

the platform version of the problem and what methods you have tried

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what result do you expect? What is the error message actually seen?