How do I get Apache to listen on ipv4 as well as ipv6?

This is how Linux is supposed to work… See:

https://unix.stackexchange.com/questions/237858/according-to-socket-statistics-apache-listens-only-on-ipv6-but-actually-serves

If you want apache2 to listen on IPv4 only, change your directive to

Listen 0.0.0.0:80

If you want apache2 to listen on IPv6 only, change your directive to

Listen [::]:80

If you want apache2 to listen on them both, change your directive to

Listen 0.0.0.0:80
Listen [::]:80

-- sw

Thank you, @stevewi! In the file
/etc/httpd/conf/httpd.conf
on my Fedora linode, I changed the line
Listen 80
to
Listen 0.0.0.0:80
and then said
systemctl restart httpd.service
netstat -at now confirms that Apache is listening on ipv4:
tcp 0 0 0.0.0.0:http 0.0.0.0:* LISTEN

But when I point a Chrome web browser at
mark.markmeretzky.com
www.markmeretzky.com
the browser says
"This site can't be reached.
mark.markmeretzky.com refused to connect."
Any ideas? Thanks again.

But when I point a Chrome web browser at
mark.markmeretzky.com
www.markmeretzky.com
the browser says
"This site can't be reached.
mark.markmeretzky.com refused to connect."
Any ideas? Thanks again.

At first, I thought it might be a DNS error but that doesn't appear to be the case:

stevewi:~ $ ping www.markmeretzky.com
PING www.markmeretzky.com (aa.bb.cc.dd): 56 data bytes
64 bytes from aa.bb.cc.dd: icmp_seq=0 ttl=38 time=86.621 ms
64 bytes from aa.bb.cc.dd: icmp_seq=1 ttl=38 time=92.012 ms
64 bytes from aa.bb.cc.dd: icmp_seq=2 ttl=38 time=86.249 ms
64 bytes from aa.bb.cc.dd: icmp_seq=3 ttl=38 time=81.260 ms
^C

stevewi:~ $ ping mark.markmeretzky.com
PING mark.markmeretzky.com (aa.bb.cc.dd): 56 data bytes
64 bytes from aa.bb.cc.dd: icmp_seq=0 ttl=38 time=83.897 ms
64 bytes from aa.bb.cc.dd: icmp_seq=1 ttl=38 time=87.708 ms
64 bytes from aa.bb.cc.dd: icmp_seq=2 ttl=38 time=95.399 ms
^C

However, IPv6 is a different story:

stevewi:~ $ ping6 www.markmeretzky.com
PING6(56=40+8+8 bytes) fe80::aaaa:bbbb:cccc:dddd%en0 --> fe80::wwww:xxxx:yyyy:zzzz
ping6: sendmsg: No route to host
ping6: wrote www.markmeretzky.com 16 chars, ret=-1
ping6: sendmsg: No route to host
ping6: wrote www.markmeretzky.com 16 chars, ret=-1
ping6: sendmsg: No route to host
ping6: wrote www.markmeretzky.com 16 chars, ret=-1
^C

stevewi:~ $ ping6 mark.markmeretzky.com
PING6(56=40+8+8 bytes) fe80::aaaa:bbbb:cccc:dddd%en0 --> fe80::wwww:xxxx:yyyy:zzzz
ping6: sendmsg: No route to host
ping6: wrote mark.markmeretzky.com 16 chars, ret=-1
ping6: sendmsg: No route to host
ping6: wrote mark.markmeretzky.com 16 chars, ret=-1
ping6: sendmsg: No route to host
ping6: wrote mark.markmeretzky.com 16 chars, ret=-1
^C

You don't have DNS A/AAAA records for either of these two domain names for your IPv6 address. If you make changes to DNS, the rule of thumb is that they take 48 hrs to propagate around the world.

My guess is that your web server configuration is messed up as well… There's no response on either IPv4 or IPv6 to either of those domains.

You can do one of two things:

• Fix your web server configuration; or
• Fix your DNS configuration for IPv6.

Frankly, I would do both.

-- sw

Thank you again, @stevewi. You're right, I created the AAAA record for IPv6 less than 48 hours ago. But for the time being, I'd be happy to just get my Apache to respond to IPv4.

netstat -tlpn confirms that my httpd is listening to port 80 with IPv4:
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 73024/httpd

lsof -nP -iTCP -sTCP:LISTEN also confirms:
httpd 73024 root 3u IPv4 709152 0t0 TCP *:80 (LISTEN)
httpd 73026 apache 3u IPv4 709152 0t0 TCP *:80 (LISTEN)
httpd 73027 apache 3u IPv4 709152 0t0 TCP *:80 (LISTEN)
httpd 73028 apache 3u IPv4 709152 0t0 TCP *:80 (LISTEN)

Ditto for ps -Af too:
root 73024 1 0 22:52 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND
apache 73025 73024 0 22:52 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND
apache 73026 73024 0 22:52 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND
apache 73027 73024 0 22:52 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND
apache 73028 73024 0 22:52 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND

I got the /etc/httpd/conf/httpd.conf file by following the instructions in https://www.linode.com/docs/guides/lamp-server-on-fedora-20/
The only change I made to this file was to change
Listen 80
to
Listen 0.0.0.0:80
and then I (logged in as root and) restarted the server with
systemctl restart httpd.service
Is there any other change I would need to make for my simple configuration? How can I find out why my Chrome web browser says
"This site [mark.markmeretzky.com] can't be reached"?

nslookup mark.markmeretzky.com and nslookup www.markmeretzky.com
give me the correct four-octet IPv4 address of my Fedora linode.

The hostname command says mark.markmeretzky.com
The /etc/logs/httpd/access_log file is empty.
Where can I look? What can I try? Thanks.

If you could post your site configuration, that would help me help you puzzle it out. Don't forget the ``` at the beginning and the end of your configuration directives so that it shows up

like this

This would probably your main site defined in /etc/apache2/apache2.conf or the VirtualHost for your main site defined in a file in /etc/apache2/sites-enabled.

-- sw

Thank you again, @stevewi. The only change I made to /etc/httpd/conf/httpd.conf was to change the Listen line to
Listen 0.0.0.0:80
The entire /etc/httpd/conf/httpd.conf is shown below.
There are no other files in the /etc/httpd/conf directory,
except one named "magic".
I haven't created any .conf files.

There is also a directory named /etc/httpd/conf.d containing three
files I haven't touched: autoindex.conf userdir.conf welcome.conf

I don't have /etc/apache2/apache2.conf or /etc/apache2/sites-enabled anywhere;
I looked for them (as root) with the commands

find / -type d -name 'apache*' 2> /dev/null
find / -name apache2.conf 2> /dev/null
find / -name 'sites-enabled' 2> /dev/null

/var/log/httpd/access_log remains empty, and I see no error messages in /var/log/httpd/error_log:

tail -5 /var/log/httpd/error_log
[Tue Mar 22 04:31:21.766171 2022] [core:notice] [pid 76380:tid 76380] SELinux policy enabled; httpd running as context system_u:system_r:httpd_t:s0
[Tue Mar 22 04:31:21.767170 2022] [suexec:notice] [pid 76380:tid 76380] AH01232: suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Tue Mar 22 04:31:21.778120 2022] [lbmethod_heartbeat:notice] [pid 76380:tid 76380] AH02282: No slotmem from mod_heartmonitor
[Tue Mar 22 04:31:21.787103 2022] [mpm_event:notice] [pid 76380:tid 76380] AH00489: Apache/2.4.52 (Fedora Linux) configured -- resuming normal operations
[Tue Mar 22 04:31:21.787124 2022] [core:notice] [pid 76380:tid 76380] AH00094: Command line: '/usr/sbin/httpd -D FOREGROUND'

Just to be clear about what I've already accomplished, and what I
want to accomplish:

I created a user named "mark" and can successfully ssh to my linode Fedora in 4 ways:
ssh mark@mark.markmeretzky.com
ssh root@mark.markmeretzky.com
ssh mark@www.markmeretzky.com
ssh root@www.markmeretzky.com

I would like to run the Apache web server on IPv4 TCP port 80,
but when I point the Chrome web browser on my Macintosh at http://www.markmeretzky.com/
or at
http://45.79.140.111/
it says "This site can't be reached--refused to connect.".

Another experiment I tried on my Macintosh was

curl http://www.markmeretzky.com/index.html
curl: (7) Failed to connect to www.markmeretzky.com port 80: Connection refused
echo $?
7

Here is the entire /etc/httpd/conf/httpd.conf file:

#
# This is the main Apache HTTP server configuration file.  It contains the
# configuration directives that give the server its instructions.
# See <URL:http://httpd.apache.org/docs/2.4/> for detailed information.
# In particular, see 
# <URL:http://httpd.apache.org/docs/2.4/mod/directives.html>
# for a discussion of each configuration directive.
#
# See the httpd.conf(5) man page for more information on this configuration,
# and httpd.service(8) on using and configuring the httpd service.
#
# Do NOT simply read the instructions in here without understanding
# what they do.  They're here only as hints or reminders.  If you are unsure
# consult the online docs. You have been warned.  
#
# Configuration and logfile names: If the filenames you specify for many
# of the server's control files begin with "/" (or "drive:/" for Win32), the
# server will use that explicit path.  If the filenames do *not* begin
# with "/", the value of ServerRoot is prepended -- so 'log/access_log'
# with ServerRoot set to '/www' will be interpreted by the
# server as '/www/log/access_log', where as '/log/access_log' will be
# interpreted as '/log/access_log'.

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

#
# Listen: Allows you to bind Apache to specific IP addresses and/or
# ports, instead of the default. See also the <VirtualHost>
# directive.
#
# Change this to Listen on a specific IP address, but note that if
# httpd.service is enabled to run at boot time, the address may not be
# available when the service starts.  See the httpd.service(8) man
# page for more information.
#
#Listen 12.34.56.78:80
#Listen 80
Listen 0.0.0.0:80
#
# Dynamic Shared Object (DSO) Support
#
# To be able to use the functionality of a module which was built as a DSO you
# have to place corresponding `LoadModule' lines at this location so the
# directives contained in it are actually available _before_ they are used.
# Statically compiled modules (those listed by `httpd -l') do not need
# to be loaded here.
#
# Example:
# LoadModule foo_module modules/mod_foo.so
#
Include conf.modules.d/*.conf

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

# 'Main' server configuration
#
# The directives in this section set up the values used by the 'main'
# server, which responds to any requests that aren't handled by a
# <VirtualHost> definition.  These values also provide defaults for
# any <VirtualHost> containers you may define later in the file.
#
# All of these directives may appear inside <VirtualHost> containers,
# in which case these default settings will be overridden for the
# virtual host being defined.
#

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

#
# ServerName gives the name and port that the server uses to identify itself.
# This can often be determined automatically, but we recommend you specify
# it explicitly to prevent problems during startup.
#
# If your host doesn't have a registered DNS name, enter its IP address here.
#
#ServerName www.example.com:80

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

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

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

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

# Further relax access to the default document root:
<Directory "/var/www/html">
    #
    # Possible values for the Options directive are "None", "All",
    # or any combination of:
    #   Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews
    #
    # Note that "MultiViews" must be named *explicitly* --- "Options All"
    # doesn't give it to you.
    #
    # The Options directive is both complicated and important.  Please see
    # http://httpd.apache.org/docs/2.4/mod/core.html#options
    # for more information.
    #
    Options Indexes FollowSymLinks

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

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

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

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

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

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

<IfModule log_config_module>
    #
    # The following directives define some format nicknames for use with
    # a CustomLog directive (see below).
    #
    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>
      # 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>

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

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

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

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

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

</IfModule>

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

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

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

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

    # For type maps (negotiated resources):
    #AddHandler type-map var

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

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

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

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

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

# Supplemental configuration
#
# Load config files in the "/etc/httpd/conf.d" directory, if any.
IncludeOptional conf.d/*.conf
[mark@mark etc]$ #
# This is the main Apache HTTP server configuration file.  It contains the
# configuration directives that give the server its instructions.
# See <URL:http://httpd.apache.org/docs/2.4/> for detailed information.
# In particular, see 
# <URL:http://httpd.apache.org/docs/2.4/mod/directives.html>
# for a discussion of each configuration directive.
#
# See the httpd.conf(5) man page for more information on this configuration,
# and httpd.service(8) on using and configuring the httpd service.
#
# Do NOT simply read the instructions in here without understanding
# what they do.  They're here only as hints or reminders.  If you are unsure
# consult the online docs. You have been warned.  
#
# Configuration and logfile names: If the filenames you specify for many
# of the server's control files begin with "/" (or "drive:/" for Win32), the
# server will use that explicit path.  If the filenames do *not* begin
# with "/", the value of ServerRoot is prepended -- so 'log/access_log'
# with ServerRoot set to '/www' will be interpreted by the
# server as '/www/log/access_log', where as '/log/access_log' will be
# interpreted as '/log/access_log'.

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

Additional information for @stevewi: Thank you again for your time.
I did another experiment. When I curl from my Macintosh, the Apache
server on my Fedora linode does not respond:

curl http://www.markmeretzky.com/index.html
curl: (7) Failed to connect to www.markmeretzky.com port 80: Connection refused
echo $?
7

But when run curl on my Fedora linode, the Apache server running there
displays the little index.html file I created in my /var/www/html
directory:

curl http://www.markmeretzky.com/index.html
<HTML>
<HEAD>
</HEAD>
<BODY>
This is my index.html test page.
</BODY>
</HTML>
echo $?
0

Additional question: when I get the Apache server to respond to the outside world, I would like to be able to point my web browser to
markmeretzky.com, not www.markmeretzky.com. How can I set that up?

I guess Fedora doesn't configure apache like every other Linuxen out there. Are you sure you need SELinux? It's going to complicate your life more than it's going to help you…

My only thoughts are:

• your problem is an artifact of SELinux; or
• port 80 is blocked in your firewall.

Look at your error_log in real time with tail -f while you're making a request. If no errors appear, there's something outside of apache blocking the request. If errors do appear, they should give you some clue as to what's wrong…

Additional question: when I get the Apache server to respond to the outside world, I would like to be able to point my web browser to markmeretzky.com, not www.markmeretzky.com. How can I set that up?

You do this with DNS A/AAAA records… You set up an A/AAAA record for markmeretzky.com pointing to your IP address and then an A/AAAA record for www pointing to the same IP address (for both your IPv4 and IPv6 addresses).

You can do this with HTTP redirects but they're not foolproof…DNS is foolproof. This makes markmeretzky.com and www.markmeretzky.com equivalent.

-- sw

Will you post the outputs from these commands please

firewall-cmd --state
firewall-cmd -V #notice capitalization
firewall-cmd --check-config
firewall-cmd --get-log-denied
Here is documentation to firewalld https://firewalld.org/documentation/man-pages/firewall-cmd.html