What Does Your User Agent Say About You?


A user agent is a computer program representing a person, for example, a browser in a Web context.

Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.

Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.

The user agent string can be accessed with JavaScript on the client side using the navigator.userAgent property.

A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".


User Agent String

Browser Data

User Agent Eff

Danielle Fletcher
• Thursday, 22 October, 2020
• 13 min read

Here at the Electronic Frontier Foundation, we have a guiding motto: “I Fight For the Users.” We didn't pick that one by accident (nor merely because we dig the 1982 classic film “Tron”), but because it provides such a clear moral compass when we sit down to work every day.



The RFC lists several ways that end-users can be involved in technical architecture decisions, and ponders the strengths and drawbacks of each: the difficulty of discussing esoteric technology with users who lack the background to understand it; the imperfection of relying on government representatives to represent the interests of their citizens (and the conflicts between those governments and the governments of other states). As the go-to group to represent users' interests with both technical depth and a genuine ethical posture.

Alas, as the RFC points out, the latest wave of Internet of Things devices have all but abandoned the idea of serving as user -agents. Instead, these sensor-studded, actuator-connected gadgets act as outposts for the corporations that sold them, sneaking around behind our backs to spy on us, corralling us into arranging our affairs to suit the manufacturer's shareholders' interests at the expense of our own.

The IETF is an Internet original, a 34-year-old institution that does the hard, unglamorous work of setting and updating standards. The “rough consensus and running code” ethic it defined gave birth to the Internet as it once was, and as it has become.

Report for Nicaragua, assessing how well the country’s mobile phone and Internet service providers (ISPs) are protecting users' personal data and communications. A few years ago, when you saw a security camera, you may have thought that the video feed went to a VCR somewhere in a back office that could only be accessed when a crime occurs.

The interruptions were caused by a macOS security service attempting to reach Apple’s Online Certificate Status Protocol (CSP) server, which had become... Cert bot uses a number of different commands (also referred to as “subcommands”) to request specific actions such as obtaining, renewing, or revoking certificates.

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The cert bot script on your web server might be named lets encrypt if your system uses an older package, or certbot-auto if you used an alternate installation method. Throughout the docs, whenever you see cert bot, swap in the correct name as needed.

Authenticators are plugins used with the cert only command to obtain a certificate. If you specify multiple domains to authenticate, they will all be listed in a single certificate.

These plugins can modify your web server’s configuration to serve your website over HTTPS using certificates obtained by cert bot. The run subcommand can also be used to specify a combination of distinct authenticator and installer plugins.

Dns-01 (53) manual Helps you obtain a certificate by giving you instructions to Http-01 (80) or dns-01 (53)Under the hood, plugins use one of several ACME protocol challenges to prove you control a domain.

The Apache plugin currently supports modern OSes based on Debian, Fedora, SUSE, Gentoo and Darwin. This automates both obtaining and installing certificates on an Apache web server.


To specify this plugin on the command line, simply include Apache. If you’re running a local web server for which you have the ability to modify the content being served, and you’d prefer not to stop the web server during the certificate issuance process, you can use the webfoot plugin to obtain a certificate by including cert only and webfoot on the command line.

In addition, you’ll need to specify --webroot-path or -w with the top-level directory (“web root”) containing the files served by your web server. Would obtain a single certificate for all of those names, using the /var/WWW/example webfoot directory for the first two, and /var/WWW/other for the second two.

The webfoot plugin works by creating a temporary file for each of your requested domains in ${webroot-path}/.well-known/acme-challenge. Then the Let’s Encrypt validation server makes HTTP requests to validate that the DNS for each requested domain resolves to the server running cert bot.

Note that to use the webfoot plugin, your server must be configured to serve files from hidden directories. The standalone plugin does not rely on any other server software running on the machine where you obtain the certificate.

It must still be possible for your machine to accept inbound connections from the Internet on the specified port using each requested domain name. On most Linux systems, IPv4 traffic will be routed to the bound IPv6 port and the failure during the second bind is expected.

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If you’d like to obtain a certificate running cert bot on a machine other than your target web server or perform the steps for domain validation yourself, you can use the manual plugin. While hidden from the UI, you can use the plugin to obtain a certificate by specifying cert only and --manual on the command line.

This requires you to copy and paste commands into another terminal session, which may be on a different computer. The HTTP challenge will ask you to place a file with a specific name and specific content in the /.well-known/acme-challenge/ directory directly in the top-level directory (“web root”) containing the files served by your web server.

When using the DNS challenge, cert bot will ask you to place a TXT DNS record with specific contents under the domain name consisting of the hostname for which you want a certificate issued, prepended by _acme-challenge. Additionally, you can specify scripts to prepare for validation and perform the authentication procedure and/or clean up after it by using the --manual-auth-hook and --manual-cleanup-hook flags.

PluginAuthInstNotes HAProxy Integration with the HAProxy load balancer s3front Integration with Amazon CloudFront distribution of S3 buckets Gandhi Obtain certificates via the Gandhi Livens API varnish Obtain certificates via a Varnish server external-auth AYA plugin for convenient scripting ritual Install certificates in ritual distributed OpenVPN servers promo Install certificates in Promo Virtualization servers dns-standalone Obtain certificates via an integrated DNS server dns-ispconfig DynDNS Authentication using Config as DNS server dns-clouddns DynDNS Authentication using Cloud DNS API dns-lightsail DynDNS Authentication using Amazon Light sail DNS API dns-inwx Hymns Authentication for In through the XML API To view a list of the certificates Cert bot knows about, run the certificates subcommand: This is a valid method of renewing a specific individual certificate.

Most users will not need to issue this command in normal circumstances. Consider using --cert-name instead of --expand, as it gives more control over which certificate is modified and it lets you remove domains as well as adding them.

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--allow-subset-of-names tells Cert bot to continue with certificate generation if only some specified domain authorizations can be obtained. The generation of a new certificate counts against several rate limits that are intended to prevent abuse of the ACME protocol, as described here.

As of version 1.10, Cert bot supports two types of private key algorithms: RSA and ECDs. If you obtain certificates using EC DSA keys, you should be careful not to downgrade your Cert bot installation since EC DSA keys are not supported by older versions of Cert bot.

Downgrades like this are possible if you switch from something like the snaps or certbot-auto to packages provided by your operating system which often lag behind. Unless you are aware that you need to support very old HTTPS clients that are not supported by most sites, you can safely just transition your site to use EC DSA keys instead of RSA keys.

If you want to use EC DSA keys for all certificates in the future, you can simply add the following line to Cert bot’s configuration file After this option is set, newly obtained certificates will use EC DSA keys.

This includes certificates managed by Cert bot that previously used RSA keys. If, however, you are aware of having a specific need to support very old TLS clients, you may want to obtain both EC DSA and RSA certificates for the same domains.

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Reasons include unspecified which is the default, as well as key compromise, affiliation changed, superseded, and cessationofoperation : Revoking a certificate will have no effect on the rate limit imposed by the Let’s Encrypt server.

Let’s Encrypt CA issues short-lived certificates (90 days). Many of the cert bot clients obtained through a distribution come with automatic renewal out of the box, such as Debian and Ubuntu versions installed through apt, CentOS/RHEL 7 through Expel, etc.

This command attempts to renew any previously-obtained certificates that expire in less than 30 days. Unlike cert only, renew acts on multiple certificates and always takes into account whether each one is near expiry.

For example, if you have a single certificate obtained using the standalone plugin, you might need to stop the web server before renewing so standalone can bind to the necessary ports, and then restart it after the plugin is finished. You can also specify hooks by placing files in subdirectories of Cert bot’s configuration directory.

One minor exception to this is if a hook specified elsewhere is simply the path to an executable file in the hook directory of the same type (e.g. your pre-book is the path to an executable in /etc/lets encrypt/renewal-hooks/PRE), the file is not run a second time. You can stop Cert bot from automatically running executables found in these directories by including --no-directory-hooks on the command line.


More information about hooks can be found by running certbot--helprenew. An alternative form that provides for more fine-grained control over the renewal process (while renewing specified certificates one at a time), is certbotcertonly with the complete set of subject domains of a specific certificate specified via -d flags.

You may also want to include the -n or --noninteractive flag to prevent blocking on user input (which is useful when running the command from iron). Please note that the CA will send notification emails to the address you provide if you do not renew certificates that are about to expire.

Cert bot is working hard to improve the renewal process, and we apologize for any inconvenience you encounter in integrating these commands into your individual environment. Certbotrenew exit status will only be 1 if a renewal attempt failed.

This means certbotrenew exit status will be 0 if no certificate needs to be updated. If you choose to modify the renewal configuration file we advise you to test its validity with the certbotrenew--dry-run command.

Modifying any files in /etc/lets encrypt can damage them so Cert bot can no longer properly manage its certificates, and we do not recommend doing so. For most tasks, it is safest to limit yourself to pointing slinks at the files there, or using --deploy-hook to copy / make new files based upon those files, if your operational situation requires it (for instance, combining certificates and keys in different way, or having copies of things with different specific permissions that are demanded by other programs).

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For example, say that a certificate’s renewal configuration file previously contained the following directives: Distributions with Automated RenewalDistribution Redistribution VersionAutomation MethodCentOSEPEL 7systemdDebianstretchcron, systemdDebiantesting/micron, systemdFedora26systemdFedora27systemdRHELEPEL 7systemdUbuntu17.10cron, systemdUbuntucertbot Patron, system All generated keys and issued certificates can be found in /etc/lets encrypt/live/domain.

Rather than copying, please point your (web) server configuration directly to those files (or create slinks). For historical reasons, the containing directories are created with permissions of 0700 meaning that certificates are accessible only to servers that run as the root user.

If you does not downgrade to an older version of Cert bot, then you can safely fix this using chmod0755/etc/lets encrypt/{live, archive}. /etc/lets encrypt/archive and /etc/lets encrypt/keys contain all previous keys and certificates, while /etc/lets encrypt/live slinks to the latest versions.

If you need other format, such as Her or PFC, then you could convert using OpenSSL. Cert bot allows for the specification of PRE and post validation hooks when run in manual mode.

When processing a validation Cert bot writes a number of lock files on your system to prevent multiple instances from overwriting each other’s changes. Additionally, if you are using Cert bot with Apache or nginx it will lock the configuration folder for that program, which are typically also in the /etc directory.

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Note that these lock files will only prevent other instances of Cert bot from using those directories, not other processes. Certificate specific configuration choices should be set in the .cone files that can be found in /etc/lets encrypt/renewal.

By default, no cli.ini file is created (though it may exist already if you installed Cert bot via a package manager, for instance). Since this configuration file applies to all invocations of cert bot it is incorrect to list domains in it.

Additionally, due to how arguments in cli.ini are parsed, options which wish to not be set should not be listed. Meaning that once 1000 files are in /var/log/lets encrypt Cert bot will delete the oldest one to make room for new logs.

Some distributions, including Debian and Ubuntu, disable cert bot’s internal log rotation in favor of a more traditional log rotate script. Cert bot supports a lot of command line options.

Rv: gecko version indicates the release version of Gecko (such as 17.0 “). The Chrome (or Chromium/Blink-based engines) user agent string is similar to Firefox’s.

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For compatibility, it adds strings like HTML, like Gecko and Safari. The Opera browser is also based on the Blink engine, which is why it almost looks the same, but adds “Or/”.

In this example, the user agent string is mobile Safari’s version. There's no “standard” way of writing an user agent string, so different web browsers use different formats (some are wildly different), and many web browsers cram loads of information into their user agents.

HTTP's specification does not limit length of headers at all. However, web-servers do limit header size they accept, throwing 413 Entity Too Large if it exceeds.

Use a dedicated table to store only Reagents (normalize it) In your related tables, store a Foreign Key value to point back to the Sergeant auto-increment primary key field Store the actual Sergeant string in a TEXT field and care not about the length Have another UNIQUE BINARY(32) (or 64, or 128 depending on your hash length) and hash the Sergeant Also enforce a maximum length in your INSERTer to keep UA strings it under 4 KB.

Coventry CodeAngry11.6k33 gold badges4242 silver badges5050 bronze badges It looks abnormal to me but I regularly see such things in logs mostly from Windows systems.

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Harry harry93111 gold badge1111 silver badges1313 bronze badges Since it's for database purposes and there is no practical limit I'd go for a Reagents Table with UserAgentId as Int and UserAgentString as NASCAR(MAX) and use a foreign key on the original table.

Assume the user agent string has no limit on its length and prepare to store such a value. In Postgres, there's a text type that accepts strings of unlimited length.

How does tracking technology follow your trail around the web, even if you’ve taken protective measures? Cover Your Tracks shows you how trackers see your browser, providing you with an overview of your unique and identifying characteristics.

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