linkchecker

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:, news:, nntp:, Telnet and local file links

  • restriction of link checking with URL filters

  • proxy support

  • username/password authorization for HTTP, FTP and Telnet

  • support for robots.txt exclusion protocol

  • support for Cookies

  • support for HTML5

  • HTML and CSS syntax check

  • 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 ~/.linkchecker/linkcheckerrc.

-h, --help

Help me! Print usage information for this program.

--stdin

Read list of white-space separated URLs to check from stdin.

-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

-D STRING, --debug=STRING

Print debugging output for the given logger. Available loggers are cmdline, checking, cache, dns, plugin and all. Specifying all is an alias for specifying all available loggers. The option can be given multiple times to debug with more than one logger. For accurate results, threading will be disabled during debug runs.

-F TYPE[/ENCODING][/FILENAME], --file-output=TYPE[/ENCODING][/FILENAME]

Output to a file linkchecker-out.TYPE, $HOME/.linkchecker/failures for failures output, 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-status

Do not print check status messages.

--no-warnings

Don’t log warnings. Default is to log warnings.

-o TYPE[/ENCODING], --output=TYPE[/ENCODING]

Specify 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.

-q, --quiet

Quiet operation, an alias for -o none. This is only useful with -F.

-v, --verbose

Log all checked URLs. Default is to log only errors and warnings.

-W REGEX, --warning-regex=REGEX

Define a regular expression which prints a warning if it matches any content of the checked link. This applies only to valid pages, so we can get their content. Use this to check for pages that contain some form of error, for example “This page has moved” or “Oracle Application error”. Note that multiple values can be combined in the regular expression, for example “(This page has moved|Oracle Application error)”. See section REGULAR EXPRESSIONS for more info.

Checking options

--cookiefile=FILENAME

Read a file with initial cookie data. 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.

-N STRING, --nntp-server=STRING

Specify an NNTP server for news: links. Default is the environment variable NNTP_SERVER. If no host is given, only the syntax of the link is checked.

--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.

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 ~/.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.

PROXY SUPPORT

To use a proxy on Unix or Windows set the http_proxy, https_proxy or ftp_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, and GNOME or KDE on Linux 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 variables to ignore any proxy settings for these domains.

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

Telnet links (telnet:)

We try to connect and if user/password are given, login to the given telnet server.

NNTP links (news:, snews:, nntp)

We try to connect to the given NNTP server. If a news group or article is specified, try to request it from the server.

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.

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.

When checking news: links the given NNTP host doesn’t need to be the same as the host of the user browsing your pages.

ENVIRONMENT

NNTP_SERVER

specifies default NNTP server

http_proxy

specifies default HTTP proxy server

ftp_proxy

specifies default FTP proxy server

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

~/.linkchecker/linkcheckerrc - default configuration file

~/.linkchecker/failures - default failures logger output filename

linkchecker-out.TYPE - default logger file output name