client.conf(5)

Name

client.conf - client configuration file for cups

Description

The client.conf file configures the CUPS client and is normally located in any of the following directories:

/etc/cups or /usr/local/etc/cups (root account)
$SNAP_COMMON/cups (snapcraft-based applications)
$HOME/.cups (historical per-user settings)
$XDG_CONFIG_HOME/cups or $HOME/.config/cups (current per-user settings)
%USERPROFILE%/AppData/Local/cups (Windows per-user settings)

Each line in the file can be a configuration directive, a blank line, or a comment. Comment lines start with the # character.

Note: macOS applications can access many of these settings in the /Library/Preferences/org.cups.PrintingPrefs.plist file instead. macOS also does not support the ServerName directive. See the NOTES section below for more information.

Directives

The following directives are understood by the client. Consult the online help for detailed descriptions:

AllowAnyRoot Yes

AllowAnyRoot No
Specifies whether to allow TLS with certificates that have not been signed by a trusted Certificate Authority. The default is Yes.

AllowExpiredCerts Yes

AllowExpiredCerts No
Specifies whether to allow TLS with expired certificates. The default is No.

DigestOptions DenyMD5

DigestOptions None
Specifies HTTP Digest authentication options. DenyMD5 disables support for the original MD5 hash algorithm. The default is None.

Encryption IfRequested

Encryption Never

Encryption Required
Specifies the level of encryption that should be used. The default is IfRequested.

BrowseDomains all

BrowseDomains none

BrowseDomains DOMAIN[,...,DOMAIN]
Specifies the DNS-SD domains to browse for IPP printers. The value all browses the ".local" domain (mDNS) and all registered DNS domains on the local system. The value none disables browsing for network printers. The default is all.

FilterLocation LOCATION[,...,LOCATION]

FilterLocation 'LOCATION'[,...,'LOCATION']

FilterLocation "LOCATION"[,...,"LOCATION"]
Specifies a list of locations to use for destinations.

FilterLocation /REGULAR-EXPRESSION/
Specifies a regular expression for matching locations to use for destinations.

FilterType any

FilterType TYPE[,...,TYPE]
Specifies the type of destinations to use. The TYPE values are "mono" for B&W printers, "color" for color printers, "duplex" for printers with 2-sided printing capabilities, "simplex" for printers with 1-sided printing capabilities, "bind" for printers that can bind output, "cover" for printers that can cover output, "punch" for printers that can punch output, "sort" for printers that can sort output, "staple" for printers with a stapler, "small" for printers that support media up to US Legal/ISO A4, "medium" for printers that support media up to US Tabloid/ISO A3, and "large" for printers that support media larger than US Tabloid/ISO A3. The default is no filtering.

ServerName HOSTNAME-OR-IP-ADDRESS[:PORT]

ServerName /DOMAIN/SOCKET
Specifies the address and optionally the port to use when connecting to the server (not supported on macOS).

ServerName HOSTNAME-OR-IP-ADDRESS[:PORT]/version=1.1
Specifies the address and optionally the port to use when connecting to a server running CUPS 1.3.12 and earlier. The default is the local spooler's domain socket.

SSLOptions [AllowDH] [AllowRC4] [AllowSSL3] [DenyCBC] [DenyTLS1.0] [MaxTLS1.0] [MaxTLS1.1] [MaxTLS1.2] [MaxTLS1.3] [MinTLS1.0] [MinTLS1.1] [MinTLS1.2] [MinTLS1.3]

SSLOptions None
Sets encryption options. The default is None which only supports encryption using TLS v1.0 or higher using known secure cipher suites. Security is reduced when Allow options are used. Security is enhanced when Deny options are used. The AllowDH option enables cipher suites using plain Diffie-Hellman key negotiation (not supported on systems using GNU TLS). The AllowRC4 option enables the 128-bit RC4 cipher suites, which are required for some older clients. The AllowSSL3 option enables SSL v3.0, which is required for some older clients that do not support TLS v1.0. The DenyCBC option disables all CBC cipher suites. The DenyTLS1.0 option disables TLS v1.0 support - this sets the minimum protocol version to TLS v1.1. The MinTLSversion options set the minimum TLS version to support. The MaxTLSversion options set the maximum TLS version to support.

TrustOnFirstUse Yes

TrustOnFirstUse No
Specifies whether to trust new (self-signed) TLS certificates by default. The default is Yes.

User NAME
Specifies the default user name to use for requests. The default is the login user name.

UserAgentTokens None

UserAgentTokens ProductOnly

UserAgentTokens Major

UserAgentTokens Minor

UserAgentTokens Minimal

UserAgentTokens OS

UserAgentTokens Full
Specifies what information is included in the User-Agent header of HTTP requests. None disables the User-Agent header. ProductOnly reports "CUPS". Major reports "CUPS/major IPP/2". Minor reports "CUPS/major.minor IPP/2.1". Minimal reports "CUPS/major.minor.patch IPP/2.1". OS reports "CUPS/major.minor.path (osname osversion) IPP/2.1". Full reports "CUPS/major.minor.path (osname osversion; architecture) IPP/2.1". The default is Minimal.

ValidateCerts Yes

ValidateCerts No
Specifies whether to only allow TLS with certificates whose commonName or subjectAltName values match the hostname of the printer or server. The default is No.

X.509 Certificate Store

CUPS uses the system root CA certificate store and per-user certificate stores managed by CUPS. The per-user certificate stores are found in /etc/cups/ssl or /usr/local/etc/cups/ssl for the root user and $XDG_CONFIG_HOME/cups/ssl or $HOME/.config/cups/ssl (Linux/*BSD), $HOME/Library/Application Support/cups/ssl (macOS), %USERPROFILE%/AppData/Local/cups (Windows), and/or $HOME/.cups/ssl (historical/other Unix platforms) for other user accounts.

Certificates, certificate signing requests, and private keys are stored as PEM-encoded files with the naming convention "COMMON-NAME.crt" for certificates, "COMMON-NAME.csr" for certificate signing requests, and "COMMON-NAME.key" for private keys. The special common name "_site_" is used for a site-specific root certificate that can be used for trust evaluations.

X.509 Certificate Validation

CUPS supports validation of the certificate's commonName and subjectAltName field values, the certificate expiration date, and the certificate's root certificate(s), if any. Self-signed certificates are "pinned" (stored) to the host in order to do validation. Validation for certain non-printing servers may add additional restrictions to the policy defined in the client.conf file. For example, OAuth authorization requires a CA-signed certificate.

The AllowAnyRoot directive controls whether unpinned self-signed certificates are acceptable. The TrustOnFirstUse directive controls whether self-certificates are automatically pinned in the per-user certificate store for subsequent host validations. When AllowAnyRoot is disabled, TrustOnFirstUse is also disabled.

Notes

Because of sandboxing, the client.conf file is not generally accessible to applications on macOS. Configuration settings can instead be viewed or changed using the defaults(1) command:

defaults write /Library/Preferences/org.cups.PrintingPrefs.plist Encryption Required
defaults write /Library/Preferences/org.cups.PrintingPrefs.plist TrustOnFirstUse -bool NO

defaults read /Library/Preferences/org.cups.PrintingPrefs.plist Encryption

On Linux and other systems using GNU TLS, the /etc/cups/ssl/site.crl or /usr/local/etc/cups/ssl/site.crl file, if present, provides a list of revoked X.509 certificates and is used when validating certificates.