Provided by: linkchecker_10.4.0-1_amd64 
NAME
linkchecker - command line client to check HTML documents and websites for broken links
SYNOPSIS
linkchecker [options] [file-or-url]...
DESCRIPTION
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
EXAMPLES
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
OPTIONS
General options
-f FILENAME, --config=FILENAME
Use FILENAME as configuration file. By default LinkChecker uses
$XDG_CONFIG_HOME/linkchecker/linkcheckerrc.
-h, --help
Help me! Print usage information for this program.
-t NUMBER, --threads=NUMBER
Generate no more than the given number of threads. Default number of threads is 10. To disable
threading specify a non-positive number.
-V, --version
Print version and exit.
--list-plugins
Print available check plugins and exit.
Output options
URL checking results
-F TYPE[/ENCODING][/FILENAME], --file-output=TYPE[/ENCODING][/FILENAME]
Output to a file linkchecker-out.TYPE, $XDG_DATA_HOME/linkchecker/failures for the failures output
type, or FILENAME if specified. The ENCODING specifies the output encoding, the default is that of
your locale. Valid encodings are listed at
https://docs.python.org/library/codecs.html#standard-encodings. The FILENAME and ENCODING parts
of the none output type will be ignored, else if the file already exists, it will be overwritten.
You can specify this option more than once. Valid file output TYPEs are text, html, sql, csv, gml,
dot, xml, sitemap, none or failures. Default is no file output. The various output types are
documented below. Note that you can suppress all console output with the option -o none.
--no-warnings
Don't log warnings. Default is to log warnings.
-o TYPE[/ENCODING], --output=TYPE[/ENCODING]
Specify the console output type as text, html, sql, csv, gml, dot, xml, sitemap, none or failures.
Default type is text. The various output types are documented below. The ENCODING specifies the
output encoding, the default is that of your locale. Valid encodings are listed at
https://docs.python.org/library/codecs.html#standard-encodings.
-v, --verbose
Log all checked URLs, overriding --no-warnings. Default is to log only errors and warnings.
Progress updates
--no-status
Do not print URL check status messages.
Application
-D STRING, --debug=STRING
Print debugging output for the given logger. Available debug loggers are cmdline, checking,
cache, plugin and all. all is an alias for all available loggers. This option can be given
multiple times to debug with more than one logger.
Quiet
-q, --quiet
Quiet operation, an alias for -o none that also hides application information messages. This is
only useful with -F, else no results will be output.
Checking options
--cookiefile=FILENAME
Use initial cookie data read from a file. The cookie data format is explained below.
--check-extern
Check external URLs.
--ignore-url=REGEX
URLs matching the given regular expression will only be syntax checked. This option can be given
multiple times. See section REGULAR EXPRESSIONS for more info.
--no-follow-url=REGEX
Check but do not recurse into URLs matching the given regular expression. This option can be
given multiple times. See section REGULAR EXPRESSIONS for more info.
--no-robots
Check URLs regardless of any robots.txt files.
-p, --password
Read a password from console and use it for HTTP and FTP authorization. For FTP the default
password is anonymous@. For HTTP there is no default password. See also -u.
-r NUMBER, --recursion-level=NUMBER
Check recursively all links up to given depth. A negative depth will enable infinite recursion.
Default depth is infinite.
--timeout=NUMBER
Set the timeout for connection attempts in seconds. The default timeout is 60 seconds.
-u STRING, --user=STRING
Try the given username for HTTP and FTP authorization. For FTP the default username is anonymous.
For HTTP there is no default username. See also -p.
--user-agent=STRING
Specify the User-Agent string to send to the HTTP server, for example "Mozilla/4.0". The default
is "LinkChecker/X.Y" where X.Y is the current version of LinkChecker.
Input options
--stdin
Read from stdin a list of white-space separated URLs to check.
FILE-OR-URL
The location to start checking with. A file can be a simple list of URLs, one per line, if the
first line is "# LinkChecker URL list".
CONFIGURATION FILES
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.
OUTPUT TYPES
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.
REGULAR EXPRESSIONS
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.
COOKIE FILES
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"
PROXY SUPPORT
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
PERFORMED CHECKS
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
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.
PLUGINS
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.
RECURSION
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.
NOTES
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.
ENVIRONMENT
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
RETURN VALUE
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.
LIMITATIONS
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.
FILES
$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
SEE ALSO
linkcheckerrc(5)
https://docs.python.org/library/codecs.html#standard-encodings - valid output encodings
https://docs.python.org/howto/regex.html - regular expression documentation
AUTHOR
Bastian Kleineidam <bastian.kleineidam@web.de>
COPYRIGHT
2000-2016 Bastian Kleineidam, 2010-2023 LinkChecker Authors
10.3.0.post33+g268799ee0 December 04, 2023 LINKCHECKER(1)