k5start (1) - Linux Man Pages
k5start: Obtain and optionally keep active a Kerberos ticket
k5start - Obtain and optionally keep active a Kerberos ticket
SYNOPSISk5start [-bFhLnPqstvx] [-c child pid file] [-f keytab]
k5start -U -f keytab [-bFhLnPqstvx] [-c child pid file]
DESCRIPTIONk5start obtains and caches an initial Kerberos 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 "sh -c command" as the command to run and quote command.
If the command contains command-line options (like "-c"), put --- on the command line before the beginning of the command to tell k5start to not parse those options as its own.
When running a command, k5start propagates HUP, TERM, INT, and QUIT signals to the child process and does not exit when those signals are received. (If the propagated signal causes the child process to exit, k5start will then exit.) This allows k5start to react properly when run under a command supervision system such as runit(8) or svscan(8) that uses signals to control supervised commands, and to run interactive commands that should receive Ctrl-C.
If a running k5start receives an ALRM signal, it immediately refreshes the ticket cache regardless of whether it is in danger of expiring.
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 this flag is given, k5start will also change directories to "/". All paths (such as to a command to run or a PID file) should therefore be given as absolute, not relative, paths.
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.
Note that on Mac OS X, the default ticket cache type is per-session and using the -b flag will disassociate k5start from the existing ticket cache. When using -b in conjunction with -K on Mac OS X, you probably also want to use the -k flag to specify a ticket cache file and force the use of a file cache.
When using this option, consider also using -L to report k5start errors to syslog.
- -c child pid file
Save the process ID (PID) of the child process into child pid file.
child pid file is created if it doesn't exist and overwritten if it
does exist. This option is only allowed when a command was given on the
command line and is most useful in conjunction with -b to allow
management of the running child process.
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).
- Do not get forwardable tickets even if the local configuration says to get forwardable tickets by default. Without this flag, k5start does whatever the library default is.
- -f keytab
- Authenticate using the keytab keytab rather than asking for a password. A key for the client principal must be present in keytab.
- -g group
- After creating the ticket cache, change its group ownership to group, which may be either the name of a group or a numeric group ID. Ticket caches are created with 0600 permissions by default, so this will have no useful effect unless used with -m.
- -H minutes
Check for a happy ticket, defined as one that has a remaining lifetime of
at least minutes minutes. If such a ticket is found, do not attempt
authentication. Instead, just run the command (if one was specified) or
exit immediately with status 0 (if none was). Otherwise, try to obtain a
new ticket and then run the command, if any. Cannot be used with -K.
If -H is used with -t, the external program will always be run even if a ticket with a sufficient remaining lifetime was found.
- Display a usage message and exit.
- -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 or less than two minutes after the next scheduled check, and gets a
new ticket if needed. If this option is not given but a command was given
on the command line, an interval appropriate for the ticket lifetime will
If an error occurs in refreshing the ticket cache, the wake-up interval will be shortened to one minute and the operation retried at that interval for as long as the error persists.
- -k ticket cache
Use ticket cache as the ticket cache rather than the contents of the
environment variable KRB5CCNAME or the library default. ticket cache
may be any ticket cache identifier recognized by the underlying Kerberos
libraries. This generally supports a path to a file, with or without a
leading "FILE:" string, but may also support other ticket cache types.
If any of -o, -g, or -m are given, ticket cache must be either a simple path to a file or start with "FILE:" or "WRFILE:".
Report messages to syslog as well as to standard output or standard error.
All messages will be logged with facility LOG_DAEMON. Regular messages
that are displayed on standard output are logged with level LOG_NOTICE.
Errors that don't cause k5start to terminate are logged with level
LOG_WARNING. Fatal errors are logged with level LOG_ERR.
This is useful when debugging problems in combination with -b.
- -l time string
- Set the ticket lifetime. time string should be in a format recognized by the Kerberos libraries for specifying times, such as "10h" (ten hours) or "10m" (ten minutes). Known units are "s", "m", "h", and "d". For more information, see kinit(1).
- -m mode
After creating the ticket cache, change its file permissions to mode,
which must be a file mode in octal (640 or 444, for example).
Setting a mode that does not allow k5start to read or write to the ticket cache will cause k5start to fail and exit when using the -K option or running a command.
- Ignored, present for option compatibility with the now-obsolete k4start.
- -o owner
- After creating the ticket cache, change its ownership to owner, which may be either the name of a user or a numeric user ID. If owner is the name of a user and -g was not also given, also change the group ownership of the ticket cache to the default group for that user.
- Do not get proxiable tickets even if the local configuration says to get proxiable tickets by default. Without this flag, k5start does whatever the library default is.
- -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).
- 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 "krbtgt", 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.
- 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 instead.
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.
If k5start has been built with AFS setpag() support and a command was given on the command line, k5start will create a new PAG before obtaining AFS tokens. Otherwise, it will obtain tokens in the current PAG.
Rather than requiring the authentication principal 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.
- Be verbose. This will print out a bit of additional information about what is being attempted and what the results are.
- Exit immediately on any error. Normally, when running a command or when run with the -K option, k5start keeps running even if it fails to refresh the ticket cache and will try again at the next check interval. With this option, k5start will instead exit.
RETURN VALUESThe 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.
EXAMPLEUse 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. k5start 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 "--" before the command to keep k5start from parsing the "-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.
ENVIRONMENTIf the environment variable AKLOG is set, its value will be used as the program to run with -t rather than the default complied into k5start. If AKLOG is not set and KINIT_PROG is set, its value will be used instead. KINIT_PROG is honored for backward compatibility but its use is not recommended due to its confusing name.
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.
FILESThe 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 "/tmp/krb5cc_%d_%s" where %d is the UID k5start is running as and %s is a random string.
AUTHORSk5start 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 [at] stanford.edu>.
Implementations of -b and -p and the example for a Debian init script are based on code contributed by Navid Golpayegani.
SEE ALSOkinit(1), krenew(1)
The kstart web page at <http://www.eyrie.org/~eagle/software/kstart/> will have the current version of k5start and krenew.