k5start - Obtain and optionally keep active a Kerberos v5 ticket.

k5start [-bnqstv] [-f keytab] [-H minutes] [-I service instance] [-i client instance] [-K minutes] [-k ticket file] [-l time string] [-p pid file] [-r service realm] [-S service name] [-u client principal] [username [command ...]]

k5start -U -f keytab [-bnqstv] [-H minutes] [-I service instance] [-K minutes] [-k ticket file] [-l time string] [-p pid file] [-r service realm] [-S service name] [command ...]

k5start obtains and caches an initial Kerberos v5 ticket-granting ticket for a principal. k5start can be used as an alternative to kinit, but it is primarily intended to be used by programs that want to use a keytab to obtain Kerberos credentials, such as a web server that needs to authenticate to another service such as an LDAP server.

Normally, the principal for which to give tickets should be specified as the first argument. username may be either just a principal name (including the optional instance) or a full principal and realm string. The -u and -i options can be used as an alternative mechanism for specifying the principal, but generally aren't as convenient. If no username is given as either the first argument or the argument to the -u option, the client principal defaults to the Unix username of the user running k5start in the default local realm.

Optionally, a command may be given on the command line of k5start. If so, that command is run after Kerberos authentication (and running aklog if desired), with the appropriate environment variables set to point it to the right ticket cache. k5start will then continue running, waking up periodically to refresh credentials slightly before they would expire, until the command completes. (The frequency with which it wakes up to refresh credentials can still be controlled with the -K option.) To run in this mode, the principal must either be specified as a regular command-line argument or via the -U option; the -u and -i options may not be used. Also, a keytab must be specified with -f to run a specific command.

The command will not be run using the shell, so if you want to use shell metacharacters in the command with their special meaning, give CWsh -c CIcommandCW as the command to run and quote command.

If the command contains command-line options (like CW-c), put on the command line before the beginning of the command to tell k5start to not parse those options as its own.

-b

After starting, detach from the controlling terminal and run in the background. This option only makes sense in combination with -K or a command that k5start will be running and can only be used if a keytab is specified with -f. k5start will not background itself until after it does the initial authentication, so that any initial errors will be reported, but it will then redirect output to /dev/null and no subsequent errors will be reported. If used in conjunction with a command to run, that command will also run in the background and will also have its input and output redirected to /dev/null. It will have to report any errors via some other mechanism for the errors to be seen.

-f keytab

Authenticate using the keytab keytab rather than asking for a password. A key for the client principal must be present in keytab.

-H minutes

Check for a happy ticket, one that has a remaining lifetime of at least minutes minutes. If such a ticket is found, exit immediately with status 0. Otherwise, try to obtain a new ticket.

-I service instance

The instance portion of the service principal. The default is the default realm of the machine. Note that unlike the client principal, a non-default service principal must be specified with -I and -S; one cannot provide the instance portion as part of the argument to -S.

-i client instance

Specifies the instance portion of the principal. This option doesn't make sense except in combination with -u. Note that the instance can be specified as part of username through the normal convention of appending a slash and then the instance, so one never has to use this option.

-K minutes

Run in daemon mode to keep a ticket alive indefinitely. The program reawakens after minutes minutes, checks if the ticket will expire before the next wakeup, and gets a new ticket if needed.

-k ticket file

Use ticket file as the ticket cache rather than the contents of the environment variable KRB5CCNAME or the library default.

-l time string

Set the ticket lifetime. time string should be in a format recognized by the Kerberos libraries for specifying times, such as CW10h (ten hours) or CW10m (ten minutes). Known units are CWs, CWm, CWh, and CWd. For more information, see kinit(1).

-n

Ignored, present for option compatibility with k4start.

-p pid file

Save the process ID (PID) of the running k5start process into pid file. pid file is created if it doesn't exist and overwritten if it does exist. This option is most useful in conjunction with -b to allow management of the running k5start daemon. Note that, when used with -b the PID file is written out after k5start is backgrounded and changes its working directory to /, so relative paths for the PID file will be relative to / (probably not what you want).

-q

Quiet. Suppresses the printing of the initial banner message saying what Kerberos principal tickets are being obtained for, and also suppresses the password prompt when the -s option is given.

-r service realm

The realm for the service principal. This defaults to the default local realm.

-S service name

Specifies the principal for which k5start is getting a service ticket. The default value is CWkrbtgt, to obtain a ticket-granting ticket. This option (along with -I) may be used if one only needs access to a single service. Note that unlike the client principal, a non-default service principal must be specified with both -S and -I; one cannot provide the instance portion as part of the argument to -S.

-s

Read the password from standard input. This bypasses the normal password prompt, which means echo isn't suppressed and input isn't forced to be from the controlling terminal. Most uses of this option are a security risk. You normally want to use a keytab and the -f option intead.

-t

Run an external program after getting a ticket. The default use of this is to run aklog to get a token. If the environment variable KINIT_PROG is set, it overrides the compiled-in default.

-U

Rather than requiring the principal to authenticate as be given on the command line, read it from the keytab specified with -f. The principal will be taken from the first entry in the keytab. -f must be specified if this option is used. When -U is given, k5start will not expect a principal name to be given on the command line, and any arguments after the options will be taken as a command to run.

-u client principal

This specifies the principal to obtain credentials as. The entire principal may be specified here, or alternatively just the first portion may be specified with this flag and the instance specified with -i. Note that there's normally no reason to use this flag rather than simply giving the principal on the command line as the first regular argument.

-v

Be verbose. This will print out a bit of additional information about what is being attempted and what the results are.

The program exits with status 0 if it successfully gets a ticket or has a happy ticket (see -H). If k5start runs aklog or some other program k5start returns the exit status of that program.

Use the /etc/krb5.keytab keytab to obtain a ticket granting ticket for the principal host/example.com, putting the ticket cache in /tmp/service.tkt. The lifetime is 10 hours and the program wakes up every 10 minutes to check if the ticket is about to expire.

    k5start -k /tmp/service.tkt -f /etc/krb5.keytab -K 10 -l 10h \
        host/example.com

Do the same, but using the default ticket cache and run the command /usr/local/bin/auth-backup. k4start will continue running until the command finishes.

    k5start -f /etc/krb5.keytab -K 10 -l 10h host/example.com \
        /usr/local/bin/auth-backup

Shows the permissions of the temporary cache file created by k5start:

    k5start -f /etc/krb5.keytab host/example.com \
        -- sh -c 'ls -l $KRB5CCNAME'

Notice the CW-- before the command to keep k5start from parsing the CW-c as its own option.

Do the same thing, but determine the principal from the keytab:

    k5start -f /etc/krb5.keytab -U -- sh -c 'ls -l $KRB5CCNAME'

Note that no principal is given before the command.

Starts k5start as a daemon using the Debian start-stop-daemon management program. This is the sort of line that one could put into a Debian init script:

    start-stop-daemon --start --pidfile /var/run/k5start.pid \
        --exec /usr/local/bin/k5start -- -b -p /var/run/k5start.pid \
        -f /etc/krb5.keytab host/example.com

This uses /var/run/k5start.pid as the PID file and obtains host/example.com tickets from the system keytab file. k5start would then be stopped with:

    start-stop-daemon --stop --pidfile /var/run/k5start.pid
    rm -f /var/run/k5start.pid

This code could be added to an init script for Apache, for example, to start a k5start process alongside Apache to manage its Kerberos credentials.

If the environment variable KINIT_PROG is set to a program (such as aklog) then this path will be used for the program to run with -t rather than the default compiled into k5start.

If no ticket file (with -k) or command is specified on the command line, k5start will use the environment variable KRB5CCNAME to determine the location of the the ticket granting ticket. If either a command is specified or the -k option is used, KRB5CCNAME will be set to point to the ticket file before running the aklog program or any command given on the command line.

The default ticket cache is determined by the underlying Kerberos libraries. The default path for aklog is determined at build time, and will normally be whichever of aklog or afslog is found in the user's path.

If a command is specified and -k was not given, k5start will create a temporary ticket cache file of the form CW/tmp/krb5cc_%d_%s where CW%d is the UID k4start is running as and CW%s is a random string.

k4start(1), kinit(1)

The kstart web page at <http://www.eyrie.org/~eagle/software/kstart/> will have the current version of k4start and k5start.

k5start was based on the k4start code written by Robert Morgan. It was ported to Kerberos v5 by Booker C. Bense. Additional cleanup and current maintenance are done by Russ Allbery <rra@stanford.edu>.

Implementations of -b and -p and the example for a Debian init script are based on code contributed by Navid Golpayegani.