1KERBEROS(7) MIT Kerberos KERBEROS(7)
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6 kerberos - Overview of using Kerberos
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9 The Kerberos system authenticates individual users in a network envi‐
10 ronment. After authenticating yourself to Kerberos, you can use Ker‐
11 beros-enabled programs without having to present passwords or certifi‐
12 cates to those programs.
13 If you receive the following response from kinit(1):
15 kinit: Client not found in Kerberos database while getting initial cre‐
17 dentials
18 you haven't been registered as a Kerberos user. See your system admin‐
20 istrator.
21 A Kerberos name usually contains three parts. The first is the pri‐
23 mary, which is usually a user's or service's name. The second is the
24 instance, which in the case of a user is usually null. Some users may
25 have privileged instances, however, such as root or admin. In the case
26 of a service, the instance is the fully qualified name of the machine
27 on which it runs; i.e. there can be an ssh service running on the ma‐
28 chine ABC (ssh/ABC@REALM), which is different from the ssh service run‐
29 ning on the machine XYZ (ssh/XYZ@REALM). The third part of a Kerberos
30 name is the realm. The realm corresponds to the Kerberos service pro‐
31 viding authentication for the principal. Realms are conventionally
32 all-uppercase, and often match the end of hostnames in the realm (for
33 instance, host01.example.com might be in realm EXAMPLE.COM).
34 When writing a Kerberos name, the principal name is separated from the
36 instance (if not null) by a slash, and the realm (if not the local
37 realm) follows, preceded by an "@" sign. The following are examples of
38 valid Kerberos names:
39 david
41 jennifer/admin
42 joeuser@BLEEP.COM
43 cbrown/root@FUBAR.ORG
44 When you authenticate yourself with Kerberos you get an initial Ker‐
46 beros ticket. (A Kerberos ticket is an encrypted protocol message that
47 provides authentication.) Kerberos uses this ticket for network utili‐
48 ties such as ssh. The ticket transactions are done transparently, so
49 you don't have to worry about their management.
50 Note, however, that tickets expire. Administrators may configure more
52 privileged tickets, such as those with service or instance of root or
53 admin, to expire in a few minutes, while tickets that carry more ordi‐
54 nary privileges may be good for several hours or a day. If your login
55 session extends beyond the time limit, you will have to re-authenticate
56 yourself to Kerberos to get new tickets using the kinit(1) command.
57 Some tickets are renewable beyond their initial lifetime. This means
59 that kinit -R can extend their lifetime without requiring you to re-au‐
60 thenticate.
61 If you wish to delete your local tickets, use the kdestroy(1) command.
63 Kerberos tickets can be forwarded. In order to forward tickets, you
65 must request forwardable tickets when you kinit. Once you have for‐
66 wardable tickets, most Kerberos programs have a command line option to
67 forward them to the remote host. This can be useful for, e.g., running
68 kinit on your local machine and then sshing into another to do work.
69 Note that this should not be done on untrusted machines since they will
70 then have your tickets.
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73 Several environment variables affect the operation of Kerberos-enabled
74 programs. These include:
75 KRB5CCNAME
77 Default name for the credentials cache file, in the form
78 TYPE:residual. The type of the default cache may determine the
79 availability of a cache collection. FILE is not a collection
80 type; KEYRING, DIR, and KCM are.
81 If not set, the value of default_ccache_name from configuration
83 files (see KRB5_CONFIG) will be used. If that is also not set,
84 the default type is FILE, and the residual is the path
85 /tmp/krb5cc_*uid*, where uid is the decimal user ID of the user.
86 KRB5_KTNAME
88 Specifies the location of the default keytab file, in the form
89 TYPE:residual. If no type is present, the FILE type is assumed
90 and residual is the pathname of the keytab file. If unset,
91 FILE:/etc/krb5.keytab will be used.
92 KRB5_CONFIG
94 Specifies the location of the Kerberos configuration file. The
95 default is /etc/krb5.conf. Multiple filenames can be specified,
96 separated by a colon; all files which are present will be read.
97 KRB5_KDC_PROFILE
99 Specifies the location of the KDC configuration file, which con‐
100 tains additional configuration directives for the Key Distribu‐
101 tion Center daemon and associated programs. The default is
102 /var/kerberos/krb5kdc/kdc.conf.
103 KRB5RCACHENAME
105 (New in release 1.18) Specifies the location of the default re‐
106 play cache, in the form type:residual. The file2 type with a
107 pathname residual specifies a replay cache file in the version-2
108 format in the specified location. The none type (residual is
109 ignored) disables the replay cache. The dfl type (residual is
110 ignored) indicates the default, which uses a file2 replay cache
111 in a temporary directory. The default is dfl:.
112 KRB5RCACHETYPE
114 Specifies the type of the default replay cache, if
115 KRB5RCACHENAME is unspecified. No residual can be specified, so
116 none and dfl are the only useful types.
117 KRB5RCACHEDIR
119 Specifies the directory used by the dfl replay cache type. The
120 default is the value of the TMPDIR environment variable, or
121 /var/tmp if TMPDIR is not set.
122 KRB5_TRACE
124 Specifies a filename to write trace log output to. Trace logs
125 can help illuminate decisions made internally by the Kerberos
126 libraries. For example, env KRB5_TRACE=/dev/stderr kinit would
127 send tracing information for kinit(1) to /dev/stderr. The de‐
128 fault is not to write trace log output anywhere.
129 KRB5_CLIENT_KTNAME
131 Default client keytab file name. If unset, FILE:/var/ker‐
132 beros/krb5/user/%{euid}/client.keytab will be used).
133 KPROP_PORT
135 kprop(8) port to use. Defaults to 754.
136 GSS_MECH_CONFIG
138 Specifies a filename containing GSSAPI mechanism module configu‐
139 ration. The default is to read /etc/gss/mech and files with a
140 .conf suffix within the directory /etc/gss/mech.d.
141 Most environment variables are disabled for certain programs, such as
143 login system programs and setuid programs, which are designed to be se‐
144 cure when run within an untrusted process environment.
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147 kdestroy(1), kinit(1), klist(1), kswitch(1), kpasswd(1), ksu(1),
148 krb5.conf(5), kdc.conf(5), kadmin(1), kadmind(8), kdb5_util(8),
149 krb5kdc(8)
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153 Steve Miller, MIT Project Athena/Digital Equipment Corporation
154 Clifford Neuman, MIT Project Athena
155 Greg Hudson, MIT Kerberos Consortium
156 Robbie Harwood, Red Hat, Inc.
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160 The MIT Kerberos 5 implementation was developed at MIT, with contribu‐
161 tions from many outside parties. It is currently maintained by the MIT
162 Kerberos Consortium.
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165 Copyright 1985, 1986, 1989-1996, 2002, 2011, 2018 Masachusetts Insti‐
166 tute of Technology
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169 MIT
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172 1985-2023, MIT
1731.21.2 KERBEROS(7)