GAI.CONF(5) Linux Programmer's Manual GAI.CONF(5)NAMEgai.conf - getaddrinfo(3) configuration file
A call to getaddrinfo(3) might return multiple answers. According to
RFC 3484 these answers must be sorted so that the answer with the high‐
est success rate is first in the list. The RFC provides an algorithm
for the sorting. The static rules are not always adequate, though.
For this reason, the RFC also requires that system administrators
should have the possibility to dynamically change the sorting. For the
glibc implementation, this can be achieved with the /etc/gai.conf file.
Each line in the configuration file consists of a keyword and its
parameters. White spaces in any place are ignored. Lines starting
with '#' are comments and are ignored.
The keywords currently recognized are:
label netmask precedence
The value is added to the label table used in the RFC 3484 sort‐
ing. If any label definition is present in the configuration
file is present, the default table is not used. All the label
definitions of the default table which are to be maintained have
to be duplicated. Following the keyword, the line has to con‐
tain a network mask and a label value.
precedence netmask precedence
This keyword is similar to label, but instead the value is
added to the precedence table as specified in RFC 3484. Once
again, the presence of a single precedence line in the configu‐
ration file causes the default table to not be used.
This keyword controls whether a process checks whether the con‐
figuration file has been changed since the last time it was
read. If the value is "yes" the file is re-read. This might
cause problems in multithreaded applications and is generally a
bad idea. The default is "no".
scopev4 mask value
Add another rule to the RFC 3484 scope table for IPv4 address.
By default, the scope IDs described in section 3.2 in RFC 3438
are used. Changing these defaults should hardly ever be neces‐
The default table according to RFC 3484 would be specified with the
following configuration file:
label ::1/128 0
label ::/0 1
label 2002::/16 2
label ::/96 3
label ::ffff:0:0/96 4
precedence ::1/128 50
precedence ::/0 40
precedence 2002::/16 30
precedence ::/96 20
precedence ::ffff:0:0/96 10
SEE ALSOgetaddrinfo(3), RFC 3484
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Linux 2013-02-13 GAI.CONF(5)