NAME¶

klog.krb5 - Authenticates to Kerberos and obtains a token

SYNOPSIS¶

klog.krb5 [-x] [-principal <user name>]
[-password <user's password>] [-cell <cell name>]
[-k <realm>] [-pipe] [-silent]
[-lifetime <ticket lifetime in hh[:mm[:ss]]>]
[-setpag] [-tmp] [-noprdb] [-unwrap] [-insecure_des]
[-help]

klog.krb5 [-x] [-pr <user name>]
[-pa <user's password>]
[-c <cell name>]
[-k <realm>] [-pi] [-si]
[-l <ticket lifetime in hh[:mm[:ss]]>]
[-se] [-t] [-n] [-u] [-i] [-h]

DESCRIPTION¶

The klog.krb5 command obtains a Kerberos v5 ticket from a Kerberos KDC and, from the ticket, an AFS token and then stores it in the Cache Manager. The Cache Manager keeps the token in kernel memory and uses it when obtaining authenticated access to the AFS filespace. This command does not affect the issuer's identity (UNIX UID) on the local file system.

By default, the command interpreter obtains a token for the AFS user name that matches the issuer's local user name. To specify an alternate user, include the -principal argument. The user named by the -principal argument does not have to appear in the local password file (the /etc/passwd file or equivalent).

By default, the command interpreter obtains a token for the local cell, as defined by the AFSCELL environment variable set in the command shell or by the /etc/openafs/ThisCell file on the local machine. To specify an alternate cell, include the -cell argument. A user can have tokens in multiple cells simultaneously, but only one token per cell per connection to the client machine. If the user's credential structure already contains a token for the requested cell, the token resulting from this command replaces it.

By default, the command interpreter obtains a Kerberos ticket for the local realm. To specify a different Kerberos realm, include the -k argument. The Kerberos realm name need not match the AFS cell name. klog.krb5 will request a ticket for the principal "afs/cell" where cell is the cell name for which the user is requesting tokens, falling back on the principal "afs" if that principal does not work.

The lifetime of the token resulting from this command is the smallest of the following:

• The maximum ticket lifetime recorded for the "afs/cell" principal in thet Kerberos database.
• The maximum ticket lifetime recorded in the specified user's Kerberos database entry.

CAUTIONS¶

By default, this command does not create a new process authentication group (PAG); see the description of the pagsh command to learn about PAGs. If a cell does not use an AFS-modified login utility, users must include -setpag option to this command, or issue the pagsh command before this one, to have their tokens stored in a credential structure that is identified by PAG rather than by local UID. Users should be aware that -setpag will not work on some systems, most notably recent Linux systems, and using pagsh is preferrable and more reliable.

When a credential structure is identified by local UID, the potential security exposure is that the local superuser "root" can use the UNIX su command to assume any other identity and automatically inherit the tokens associated with that UID. Identifying the credential structure by PAG makes it more difficult (but not impossible) for the local superuser to obtain tokens of other users.

If the -password argument is used, the specified password cannot begin with a hyphen, because it is interpreted as another option name. Use of the -password argument is not recommended in any case.

By default, it is possible to issue this command on a properly configured NFS client machine that is accessing AFS via the NFS/AFS Translator, assuming that the NFS client machine is a supported system type. However, if the translator machine's administrator has enabled UID checking by including the -uidcheck on argument to the fs exportafs command, the command fails with an error message similar to the following:

   Warning: Remote pioctl to <translator_machine> has failed (err=8). . .
   Unable to authenticate to AFS because a pioctl failed.

Enabling UID checking means that the credential structure in which tokens are stored on the translator machine must be identified by a UID that matches the local UID of the process that is placing the tokens in the credential structure. After the klog.krb5 command interpreter obtains the token on the NFS client, it passes it to the remote executor daemon on the translator machine, which makes the system call that stores the token in a credential structure on the translator machine. The remote executor generally runs as the local superuser "root", so in most cases its local UID (normally zero) does not match the local UID of the user who issued the klog.krb5 command on the NFS client machine.

Issuing the klog.krb5 command on an NFS client machine creates a security exposure: the command interpreter passes the token across the network to the remote executor daemon in clear text mode.

OPTIONS¶

-x

Appears only for backwards compatibility. Its former function is now the default behavior of this command.

-principal <user name>

Specifies the user name to authenticate. If this argument is omitted, the default value is the local user name.

-password <user's password>

Specifies the issuer's password (or that of the alternate user identified by the -principal argument). Omit this argument to have the command interpreter prompt for the password, in which case it does not echo visibly in the command shell.

-cell <cell name>

Specifies the cell for which to obtain a token. During a single login session on a given machine, a user can be authenticated in multiple cells simultaneously, but can have only one token at a time for each of them (that is, can only authenticate under one identity per cell per session on a machine). It is acceptable to abbreviate the cell name to the shortest form that distinguishes it from the other cells listed in the /etc/openafs/CellServDB file on the client machine on which the command is issued.

If this argument is omitted, the command is executed in the local cell, as defined

-k <realm>

Obtain tickets and tokens from the <realm> Kerberos realm. If this option is not given, klog.krb5 defaults to using the default local realm. The Kerberos realm name need not match the AFS cell name.

-pipe

Suppresses all output to the standard output stream, including prompts and error messages. The klog.krb5 command interpreter expects to receive the password from the standard input stream. Do not use this argument; it is designed for use by application programs rather than human users.

-silent

Suppresses some of the trace messages that the klog.krb5 command produces on the standard output stream by default. It still reports on major problems encountered.

-lifetime <ticket lifetime

This option is not implemented by klog.krb5 and has no effect.

-setpag

Creates a process authentication group (PAG) prior to requesting authentication. The token is associated with the newly created PAG.

-tmp

Creates a Kerberos-style ticket file rather than only obtaining tokens. The ticket file will be stored in the default Kerberos ticket cache location, which is usually in the /tmp directory of the local machine (but depends on the Kerberos implementation used).

-noprdb

By default, klog.krb5 looks up the user's AFS ID in the Protection Server and associates the token with that AFS ID. This is helpful when looking at the output of commands like tokens but is not required. If this option is given, this behavior is suppressed and klog.krb5 will store the token under a generic name. You may wish this if, for example, you have problems contacting the Protection Server for an AFS cell for some reason.

-unwrap

Normally, klog.krb5 uses the Kerberos service ticket for the AFS principal as the AFS token. If this option is given, klog.krb5 creates a different, simplified AFS token form based on the service ticket (the so-called "rxkad 2b" token). Normally, this is not necessary. However, if you are using older OpenAFS software that cannot handle large ticket sizes in conjunction with Active Directory as the Kerberos server, using -unwrap can shrink the AFS token size so that older software can handle it more easily.

-insecure_des

Configures libkrb5 to allow the use of the (insecure) single-DES encryption types. When rxkad-k5 is in use, this is not needed.

-help

Prints the online help for this command. All other valid options are ignored.

OUTPUT¶

If the -tmp flag is included, the following message confirms that a Kerberos ticket cache was created:

   Wrote ticket file to /tmp/krb5cc_1000_rENJoZ

The path to the cache will vary, of course.

EXAMPLES¶

Most often, this command is issued without arguments. The appropriate password is for the person currently logged into the local system. The ticket's lifetime is calculated as described in "DESCRIPTION".

   % klog.krb5
   Password for user@EXAMPLE.ORG:

The following example authenticates the user as admin in the Example Corporation's test cell:

   % klog.krb5 -principal admin -cell test.example.com
   Password for admin@EXAMPLE.COM:

PRIVILEGE REQUIRED¶

None

SEE ALSO¶

aklog(1), fs_exportafs(1), pagsh(1), tokens(1)

COPYRIGHT¶

IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.

This documentation is covered by the IBM Public License Version 1.0. It was converted from HTML to POD by software written by Chas Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.