linkchecker - Man Page

• Find broken links on https://example.com/: linkchecker https://example.com/
• Also check URLs that point to external domains: linkchecker --check-extern https://example.com/
• Ignore URLs that match a specific regular expression: linkchecker --ignore-url regular_expression https://example.com/
• Output results to a CSV file: linkchecker --file-output csv/path/to/file https://example.com/

tldr.sh

linkchecker [options] [file-or-url]...

LinkChecker features

• recursive and multithreaded checking
• output in colored or normal text, HTML, SQL, CSV, XML or a sitemap graph in different formats
• support for HTTP/1.1, HTTPS, FTP, mailto: and local file links
• restriction of link checking with URL filters
• proxy support
• username/password authorization for HTTP and FTP
• support for robots.txt exclusion protocol
• support for Cookies
• support for HTML5
• Antivirus check
• a command line and web interface

The most common use checks the given domain recursively:

$ linkchecker http://www.example.com/

Beware that this checks the whole site which can have thousands of URLs. Use the -r option to restrict the recursion depth.

Don't check URLs with /secret in its name. All other links are checked as usual:

$ linkchecker --ignore-url=/secret mysite.example.com

Checking a local HTML file on Unix:

$ linkchecker ../bla.html

Checking a local HTML file on Windows:

C:\> linkchecker c:empest.html

You can skip the http:// url part if the domain starts with www.:

$ linkchecker www.example.com

You can skip the ftp:// url part if the domain starts with ftp.:

$ linkchecker -r0 ftp.example.com

Generate a sitemap graph and convert it with the graphviz dot utility:

$ linkchecker -odot -v www.example.com | dot -Tps > sitemap.ps

Configuration files can specify all options above. They can also specify some options that cannot be set on the command line. See linkcheckerrc(5) for more info.

Note that by default only errors and warnings are logged. You should use the option --verbose to get the complete URL list, especially when outputting a sitemap graph format.

text

Standard text logger, logging URLs in keyword: argument fashion.

html

Log URLs in keyword: argument fashion, formatted as HTML. Additionally has links to the referenced pages. Invalid URLs have HTML and CSS syntax check links appended.

csv

Log check result in CSV format with one URL per line.

gml

Log parent-child relations between linked URLs as a GML sitemap graph.

dot

Log parent-child relations between linked URLs as a DOT sitemap graph.

gxml

Log check result as a GraphXML sitemap graph.

xml

Log check result as machine-readable XML.

sitemap

Log check result as an XML sitemap whose protocol is documented at https://www.sitemaps.org/protocol.html.

sql

Log check result as SQL script with INSERT commands. An example script to create the initial SQL table is included as create.sql.

failures

Suitable for cron jobs. Logs the check result into a file $XDG_DATA_HOME/linkchecker/failures which only contains entries with invalid URLs and the number of times they have failed.

none

Logs nothing. Suitable for debugging or checking the exit code.

LinkChecker accepts Python regular expressions. See https://docs.python.org/howto/regex.html for an introduction. An addition is that a leading exclamation mark negates the regular expression.

A cookie file contains standard HTTP header (RFC 2616) data with the following possible names:

Host (required)

Sets the domain the cookies are valid for.

Path (optional)

Gives the path the cookies are value for; default path is /.

Set-cookie (required)

Set cookie name/value. Can be given more than once.

Multiple entries are separated by a blank line. The example below will send two cookies to all URLs starting with http://example.com/hello/ and one to all URLs starting with https://example.org/:

Host: example.com
Path: /hello
Set-cookie: ID="smee"
Set-cookie: spam="egg"

Host: example.org
Set-cookie: baggage="elitist"; comment="hologram"

To use a proxy on Unix or Windows set the http_proxy or https_proxy environment variables to the proxy URL. The URL should be of the form http://[user:pass@]host[:port]. LinkChecker also detects manual proxy settings of Internet Explorer under Windows systems. On a Mac use the Internet Config to select a proxy. You can also set a comma-separated domain list in the no_proxy environment variable to ignore any proxy settings for these domains. The curl_ca_bundle environment variable can be used to identify an alternative certificate bundle to be used with an HTTPS proxy.

Setting a HTTP proxy on Unix for example looks like this:

$ export http_proxy="http://proxy.example.com:8080"

Proxy authentication is also supported:

$ export http_proxy="http://user1:mypass@proxy.example.org:8081"

Setting a proxy on the Windows command prompt:

C:\> set http_proxy=http://proxy.example.com:8080

All URLs have to pass a preliminary syntax test. Minor quoting mistakes will issue a warning, all other invalid syntax issues are errors. After the syntax check passes, the URL is queued for connection checking. All connection check types are described below.

HTTP links (http:, https:)

After connecting to the given HTTP server the given path or query is requested. All redirections are followed, and if user/password is given it will be used as authorization when necessary. All final HTTP status codes other than 2xx are errors.

HTML page contents are checked for recursion.

Local files (file:)

A regular, readable file that can be opened is valid. A readable directory is also valid. All other files, for example device files, unreadable or non-existing files are errors.

HTML or other parseable file contents are checked for recursion.

Mail links (mailto:)

A mailto: link eventually resolves to a list of email addresses. If one address fails, the whole list will fail. For each mail address we check the following things:

1. Check the address syntax, both the parts before and after the @ sign.
2. Look up the MX DNS records. If we found no MX record, print an error.
3. Check if one of the mail hosts accept an SMTP connection. Check hosts with higher priority first. If no host accepts SMTP, we print a warning.
4. Try to verify the address with the VRFY command. If we got an answer, print the verified address as an info.

FTP links (ftp:)

For FTP links we do:

1. connect to the specified host
2. try to login with the given user and password. The default user is anonymous, the default password is anonymous@.
3. try to change to the given directory
4. list the file with the NLST command

Unsupported links (javascript:, etc.)

An unsupported link will only print a warning. No further checking will be made.

The complete list of recognized, but unsupported links can be found in the linkcheck/checker/unknownurl.py source file. The most prominent of them should be JavaScript links.

Sitemaps are parsed for links to check and can be detected either from a sitemap entry in a robots.txt, or when passed as a FILE-OR-URL argument in which case detection requires the urlset/sitemapindex tag to be within the first 70 characters of the sitemap. Compressed sitemap files are not supported.

There are two plugin types: connection and content plugins. Connection plugins are run after a successful connection to the URL host. Content plugins are run if the URL type has content (mailto: URLs have no content for example) and if the check is not forbidden (ie. by HTTP robots.txt). Use the option --list-plugins for a list of plugins and their documentation. All plugins are enabled via the linkcheckerrc(5) configuration file.

Before descending recursively into a URL, it has to fulfill several conditions. They are checked in this order:

1. A URL must be valid.
2. A URL must be parseable. This currently includes HTML files, Opera bookmarks files, and directories. If a file type cannot be determined (for example it does not have a common HTML file extension, and the content does not look like HTML), it is assumed to be non-parseable.
3. The URL content must be retrievable. This is usually the case except for example mailto: or unknown URL types.
4. The maximum recursion level must not be exceeded. It is configured with the --recursion-level option and is unlimited per default.
5. It must not match the ignored URL list. This is controlled with the --ignore-url option.
6. The Robots Exclusion Protocol must allow links in the URL to be followed recursively. This is checked by searching for a "nofollow" directive in the HTML header data.

Note that the directory recursion reads all files in that directory, not just a subset like index.htm.

URLs on the commandline starting with ftp. are treated like ftp://ftp., URLs starting with www. are treated like http://www.. You can also give local files as arguments. If you have your system configured to automatically establish a connection to the internet (e.g. with diald), it will connect when checking links not pointing to your local host. Use the --ignore-url option to prevent this.

Javascript links are not supported.

If your platform does not support threading, LinkChecker disables it automatically.

You can supply multiple user/password pairs in a configuration file.

http_proxy

specifies default HTTP proxy server

https_proxy

specifies default HTTPS proxy server

curl_ca_bundle

an alternative certificate bundle to be used with an HTTPS proxy

no_proxy

comma-separated list of domains to not contact over a proxy server

LC_MESSAGES, LANG, LANGUAGE

specify output language

The return value is 2 when

• a program error occurred.

The return value is 1 when

• invalid links were found or
• link warnings were found and warnings are enabled

Else the return value is zero.

LinkChecker consumes memory for each queued URL to check. With thousands of queued URLs the amount of consumed memory can become quite large. This might slow down the program or even the whole system.

$XDG_CONFIG_HOME/linkchecker/linkcheckerrc - default configuration file

$XDG_DATA_HOME/linkchecker/failures - default failures logger output filename

linkchecker-out.TYPE - default logger file output name

linkcheckerrc(5)

https://docs.python.org/library/codecs.html#standard-encodings - valid output encodings

https://docs.python.org/howto/regex.html - regular expression documentation

Bastian Kleineidam <bastian.kleineidam@web.de>

2000-2016 Bastian Kleineidam, 2010-2024 LinkChecker Authors

linkcheckerrc(5).