\" Id: logging.mdoc,v 1.3 2004/03/09 06:30:08 marka Exp
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\" The following six UNCOMMENTED lines are required.
Dd January 1, 1996
\"Os OPERATING_SYSTEM [version/release]
Os BSD 4
\"Dt DOCUMENT_TITLE [section number] [volume]
Dt LOGGING @SYSCALL_EXT@
Sh NAME
Nm log_open_stream ,
Nm log_close_stream ,
Nm log_get_stream ,
Nm log_get_filename ,
Nm log_vwrite ,
Nm log_write ,
Nm log_new_context ,
Nm log_free_context ,
Nm log_add_channel ,
Nm log_remove_channel ,
Nm log_option ,
Nm log_category_is_active ,
Nm log_new_syslog_channel ,
Nm log_new_file_channel ,
Nm log_set_file_owner ,
Nm log_new_null_channel ,
Nm log_inc_references ,
Nm log_dec_references ,
Nm log_free_channel
Nd logging system
Sh SYNOPSIS
Fd #include <isc/logging.h>
Ft FILE *
Fn log_open_stream "log_channel chan"
Ft int
Fn log_close_stream "log_channel chan"
Ft FILE *
Fn log_get_stream "log_channel chan"
Ft char *
Fn log_get_filename "log_channel chan"
Ft void
Fn log_vwrite "log_context lc" "int category" "int level" \
   "const char *format" va_list args"
Ft void
Fn log_write "log_context lc" "int category" "int level" \
   "const char *format" "..."
Ft int
Fn log_check_channel "log_context lc" "int level" "log_channel chan"
Ft int
Fn log_check "log_context lc" "int category" "int level"
Ft int
Fn log_new_context "int num_categories" "char **category_names" \
   "log_context *lc"
Ft void
Fn log_free_context "log_context lc"
Ft int
Fn log_add_channel "log_context lc" "int category" "log_channel chan"
Ft int
Fn log_remove_channel "log_context lc" "int category" "log_channel chan"
Ft int
Fn log_option "log_context lc" "int option" "int value"
Ft int
Fn log_category_is_active "log_context lc" "int category"
Ft log_channel
Fn log_new_syslog_channel "unsigned int flags" "int level" "int facility"
Ft log_channel
Fn log_new_file_channel "unsigned int flags" "int level" \
   "char *name" "FILE *stream" "unsigned int versions" \
   "unsigned long max_size"
Ft int
Fn log_set_file_owner "log_channel chan" "uid_t owner" "gid_t group"
Ft log_channel
Fn log_new_null_channel "void"
Ft int
Fn log_inc_references "log_channel chan"
Ft int
Fn log_dec_references "log_channel chan"
Ft int
Fn log_free_channel "log_channel chan"
Sh DESCRIPTION
The
Sy ISC
Nm logging library
is flexible logging system which is based upon a set of concepts:
Nm logging channels ,
Nm categories ,
and
Nm logging contexts .
Pp
The basic building block is the
Dq Nm logging channel ,
which includes a
Nm priority
(logging level), which type of logging is to occur, and other
flags and information associated with technical aspects of the logging.
The set of priorities which are supported is shown below, in the section
Sx Message Priorities .
A priority sets a threshold for message logging; a logging channel will
Em only
log those messages which are
Em at least as important
as its priority indicates.  (The fact that
Dq more important
means
Dq more negative ,
under the current scheme, is an implementation detail; if a channel has
a priority of
Dv log_error ,
then it will
Em not
log messages with the
Dv log_warning
priority, but it
Em will
log messages with the
Dv log_error
or
Dv log_critical
priority.)
Pp
The
Nm logging channel
also has an indication of the type of logging performed.  Currently,
the supported
Nm logging types
include (see also
Sx Logging Types ,
below):
Bl -tag -width "log_syslog" -compact -offset indent
It Dv log_syslog
for
Xr syslog 3 Ns -style
logging
It Dv log_file
for use of a file
It Dv log_null
for
Em no
logging
El
A new logging channel is created by calling either
Fn log_new_syslog_channel ,
Fn log_new_file_channel ,
or
Fn log_new_null_channel ,
respectively.
When a channel is no longer to be used, it can be freed using
Fn log_free_channel .
Pp
Both
Dv log_syslog
and
Dv log_file
channel types can include more information; for instance, a
Dv log_syslog Ns -type
channel allows the specification of a
Xr syslog 3 Ns -style
Dq facility ,
and a
Dv log_file Ns -type
channels allows the caller to set a maximum file size and number
of versions.  (See
Fn log_new_syslog_channel
or
Fn log_new_file_channel ,
below.)
Additionally, once a logging channel of type
Dv log_file
is defined, the functions
Fn log_open_stream
and
Fn log_close_stream
can open or close the stream associated with the logging channel's logging
filename.  The
Fn log_get_stream
and
Fn log_get_filename
functions return the stream or filename, respectively, of such a logging
channel.  Also unique to logging channels of type
Dv log_file
is the
Fn log_set_file_owner
function, which tells the logging system what user and group ought to own
newly created files (which is only effective if the caller is privileged.)
Pp
Callers provide
Dq Nm categories ,
determining both the number of such categories and any (optional) names.
Categories are like array indexes in C; if the caller declares
Dq Va n
categories, then they are considered to run from 0 to
Va n-1 ;
with this scheme, a category number would be invalid if it were negative or
greater than/equal to
Va n .
Each category can have its own list of
Nm logging channels
associated with it; we say that such a channel is
Dq in
the particular category.
Sy NOTE :
Individual logging channels can appear in more than one category.
Pp
A
Dq Nm logging context
is the set of all
Nm logging channels
associated with the context's
Nm categories ;
thus, a particular
Nm category
scheme is associated with a particular
Nm logging context .
Sy NOTE :
A logging channel may appear in more than one logging context, and in
multiple categories within each logging context.
Pp
Use
Fn log_add_channel
and
Fn log_remove_channel
to add or remove a logging channel to some category in a logging context.
To see if a given category in a logging context is being used, use the
Boolean test
Fn log_category_is_active .
Pp
A
Nm logging context
can also have a
Nm priority
(logging level)
and various flags associated with the whole context; in order to alter the
flags or change the priority of a context, use
Fn log_option .
Ss Message Priorities
Currently, five
Nm priorities
(logging levels) are supported (they can also be found in the header file):
Bd -literal -offset indent
#define log_critical            (-5)
#define log_error               (-4)
#define log_warning             (-3)
#define log_notice              (-2)
#define log_info                (-1)
Ed
Pp
In the current implementation, logging messages which have a level greater
than 0 are considered to be debugging messages.
Ss Logging Types
The three different
Nm logging types
currently supported are different values of the enumerated type
Ft log_output_type
(these are also listed in the header file):
Bd -literal -offset indent
typedef enum { log_syslog, log_file, log_null } log_output_type;
Ed
Ss Logging Channel Flags
There are several flags which can be set on a logging channel; the flags
and their meanings are as follows (they are also found in the header file):
Bl -tag -width "LOG_USE_CONTEXT_LEVEL  " -offset indent
It Dv LOG_CHANNEL_BROKEN
This is set only when some portion of
Fn log_open_stream
fails:
Xr open 2
or
Xr fdopen 3
fail;
Xr stat 2
fails in a
Dq bad
way; versioning or truncation is requested on a non-normal file.
It Dv LOG_CHANNEL_OFF
This is set for channels opened by
Fn log_new_null_channel .
It Dv LOG_CLOSE_STREAM
If this flag is set, then
Fn log_free_channel
will free a
No non- Dv NULL
stream of a logging channel which is being
Xr free 3 Ns -d
(if the logging channel is of type
Dv log_file ,
of course).
It Dv LOG_PRINT_CATEGORY
If set,
Fn log_vwrite
will insert the category name, if available, into logging messages which are
logged to channels of type
Dv log_syslog
or
Dv log_file .
It Dv LOG_PRINT_LEVEL
If set,
Fn log_vwrite
will insert a string identifying the message priority level into the
information logged to channels of type
Dv log_syslog
or
Dv log_file .
It Dv LOG_REQUIRE_DEBUG
Only log debugging messages (i.e., those with a priority greater than zero).
It Dv LOG_TIMESTAMP
If set,
Fn log_vwrite
will insert a timestamp into logging messages which are logged to channels of
type
Dv log_syslog
or
Dv log_file .
It Dv LOG_TRUNCATE
Truncate logging file when re-opened
Fn ( log_open_stream
will
Xr unlink 2
the file and then
Xr open 2
a new file of the same name with the
Dv O_EXCL
bit set).
It Dv LOG_USE_CONTEXT_LEVEL
Use the logging context's priority or logging level, rather than the logging
channel's own priority.  This can be useful for those channels which are
included in multiple logging contexts.
El
Ss FUNCTION DESCRIPTIONS
The function
Fn log_open_stream
is for use with channels which log to a file; i.e., logging channels with a
Va type
field set to
Dq Dv log_file .
If the logging channel pointed to by
Dq Fa chan
is valid, it attempts to open (and return) the stream associated with that
channel.  If the stream is already opened, then it is returned; otherwise,
Xr stat 2
is used to test the filename for the stream.
Pp
At this point, if the logging file is supposed to have different
Va versions
(i.e., incremented version numbers; higher numbers indicate older versions
of the logging file).  If so, then any existing versions are
Xr rename 2 Ns -d
to have one version-number higher than previously, and the
Dq current
filename for the stream is set to the
Dq \&.0
form of the name.  Next, if the logging file is supposed to be truncated
(i.e., the
Dv LOG_TRUNCATE
bit of the
Va flags
field of the logging channel structure is set), then any file with the
Dq current
filename for the stream is
Xr unlink 2 Ns -d .
Sy NOTE :
If the logging file is
Em not
a regular file, and either of the above operations (version numbering
or truncation) is supposed to take place, a
Dv NULL
file pointer is returned.
Pp
Finally, the filename associated with the logging channel is
Xr open 2 Ns -d
using the appropriate flags and a mode which sets the read/write permissions
for the user, group, and others.  The file descriptor returned by
Xr open 2
is then passed to
Xr fopen 3 ,
with the append mode set, and the stream returned by this call is stored
in the
Fa chan
structure and returned.
Pp
If
Fn log_open_stream
fails at any point, then the
Dv LOG_CHANNEL_BROKEN
bit of the
Va flags
field of the logging channel pointed to by
Fa chan
is set, a
Dv NULL
is returned, and
Va errno
contains pertinent information.
Pp
The
Fn log_close_stream
function closes the stream associated with the logging channel pointed to by
Dq Fa chan
(if
Fa chan
is valid and the stream exists and can be closed properly by
Xr fclose 3 ) .
The stream is set to
Dv NULL
even if the call to
Xr fclose 3
fails.
Pp
The function
Fn log_get_stream
returns the stream associated with the logging channel pointed to by
Dq Fa chan ,
if it is
No non- Ns Dv NULL
and specifies a logging channel which has a
Dv FILE *
or stream associated with it.
Pp
The
Fn log_get_filename
function returns the name of the file associated with the logging channel
pointed to by
Dq Fa chan ,
if it is
No non- Ns Dv NULL
and specifies a logging channel which has a file associated with it.
Pp
The
Fn log_vwrite
function performs the actual logging of a message to the various logging
channels of a logging context
Fa lc .
The message consists of an
Xr fprint 3 Ns -style
Fa format
and its associated
Fa args
(if any); it will be written to all logging channels in the given
Fa category
which have a priority set to
Fa level
or any
Em less important
priority value.  If the
Fa category
is not valid or has no logging channels, then the category defaults to 0.
Pp
There are a number of conditions under which a call to
Fn log_vwrite
will not result in actually logging the message: if there is no logging channel
at even the default category (0), or if a given channel is either
Dq broken
or
Dq off
(i.e., its flags have
Dv LOG_CHANNEL_BROKEN
or
Dv LOG_CHANNEL_OFF
set, respectively), or if the logging channel channel is of type
Dv log_null .
Additionally, if the logging channel's flag has
Dv LOG_REQUIRE_DEBUG
set and the message is not a debugging message (i.e., has a level greater
than 0), then it will not be logged.
Finally, if the message's priority is less important than the
channel's logging level (the priority threshold), will not be logged.
Sy NOTE :
If a logging channel's flag has
Dv LOG_USE_CONTEXT_LEVEL
set, it will use the logging context's priority, rather than its own.
Pp
If all of these hurdles are passed, then only
Dv log_syslog
and
Dv log_file
channels actually can have logging.  For channels which use
Xr syslog 3 ,
the channel's
Xr syslog 3
facility is used in conjunction with a potentially modified form of the
message's priority level, since
Xr syslog 3
has its own system of priorities
Pq Pa /usr/include/syslog.h .
All debug messages (priority >= 0) are mapped to
Xr syslog 3 Ns 's
Dv LOG_DEBUG
priority, all messages
Dq more important
than
Dv log_critical
are mapped to
Dv LOG_CRIT ,
and the priorities corresponding to the ones listed in the section
Sx Message Priorities
are given the obvious corresponding
Xr syslog 3
priority.
Pp
For
Dv log_file
type logging channels, if the file size is greater than the maximum file
size, then no logging occurs.  (The same thing happens if a
Dv NULL
stream is encountered and
Fn log_open_stream
fails to open the channel's stream.)
Pp
For both logging to normal files and logging via
Xr syslog 3 ,
the value of the flags
Dv LOG_TIMESTAMP ,
Dv LOG_PRINT_CATEGORY ,
and
Dv LOG_PRINT_LEVEL
are used in determining whether or not these items are included in the logged
information.
Pp
The
Fn log_write
function is merely a front-end to a call to
Fn log_vwrite ;
see the description of that function, above, for more information.
Pp
Fn log_check
and
Fn log_check_channel
are used to see if a contemplated logging call will actually generate any
output, which is useful when creating a log message involves non-trivial
work.
Fn log_check
will return non-zero if a call to
Fn log_vwrite
with the given
Fa category
and
Fa level
would generate output on any channels, and zero otherwise.
Fn log_check_channel
will return non-zero if writing to the
Fa chan
at the given
Fa level
would generate output.
Pp
The function
Fn log_new_context
creates a new
Nm logging context ,
and stores this in the
Dq Va opaque
field of the argument
Dq Fa lc ,
and opaque structure used internally.  This new
Nm context
will include the
Dq Fa num_categories
and
Dq Fa category_names
which are supplied; the latter can be
Dv NULL .
Sy NOTE :
Since
Dq Fa category_names
is used directly, it
Em must not
be freed by the caller, if it is
No non- Ns Dv NULL .
The initial logging flags and priority are both set to zero.
Pp
The
Fn log_free_context
function is used to free the opaque structure
Dq Va lc.opaque
and its components.
Sy NOTE :
The
Dq Va opaque
field of
Dq Fa lc
Em must
be
No non- Ns Dv NULL .
For each of the various
Dq categories
(indicated by the
Dq Va num_categories
which were in the corresponding call to
Fn log_new_context )
associated with the given
Nm logging context ,
Em all
of the
Nm logging channels
are
Xr free 3 Ns -d .
The opaque structure itself is then
Xr free 3 Ns -d ,
and
Dq Va lc.opaque
is set to
Dv NULL .
Pp
Sy NOTE :
The function
Fn log_free_context
does
Em not
free the memory associated with
Fa category_names ,
since the logging library did not allocate the memory for it, originally;
it was supplied in the call to
Fn log_new_context .
Pp
The function
Fn log_add_channel
adds the
Nm logging channel
Dq Fa chan
to the list of logging channels in the given
Fa category
of the
Nm logging context
Dq Fa lc .
No checking is performed to see whether or not
Fa chan
is already present in the given
Fa category ,
so multiple instances in a single
Fa category
can occur (but see
Fn log_remove_channel ,
below).
Pp
The
Fn log_remove_channel
function
removes
Em all
occurrences of the
Nm logging channel
Dq Fa chan
from the list of logging channels in the given
Fa category
of the
Nm logging context
Dq Fa lc .
It also attempts to free the channel by calling
Fn log_free_channel
(see its description, below).
Pp
The
Fn log_option
function is used to change the
Fa option
of the indicated logging context
Fa lc
to the given
Fa value .
The
Fa option
can be either
Dv LOG_OPTION_LEVEL
or
Dv LOG_OPTION_DEBUG ;
in the first case, the log context's debugging level is reset to the
indicated level.  If the
Fa option
is
Dv LOG_OPTION_DEBUG ,
then a non-zero
Fa value
results in setting the debug flag of the logging context, while a zero
Fa value
means that the debug flag is reset.
Pp
The
Fn log_category_is_active
test returns a 1 if the given
Fa category
of the indicated logging context
Fa lc
has at least one logging channel, and 0, otherwise.
Pp
The functions
Fn log_new_syslog_channel ,
Fn log_new_file_channel ,
and
Fn log_new_null_channel
create a new channel of the type specified (thus, the difference in arguments);
the
Dq Va type
field of the new
Do
Ft struct log_channel
Dc
is always set to the appropriate value.
Pp
The
Fn log_new_syslog_channel
function
Xr malloc 3 Ns -s
a new
Ft struct log_channel
of
Va type
Dv log_syslog ,
i.e., a logging channel which will use
Xr syslog 3 .
The new structure is filled out with the
Dq Fa flags ,
Dq Fa level ,
and
Dq Fa facility
which are given; the
Va references
field is initialized to zero.
See
Sx Logging Channel Flags
and
Sx Message Priorities ,
above, or the header file for information about acceptable values for
Dq Fa flags ,
and
Dq Fa level .
The
Dq Fa facility .
can be any valid
Xr syslog 3
facility; see the appropriate system header file or manpage for more
information.
Pp
Ft log_channel
Fn log_new_file_channel "unsigned int flags" "int level" \
   "char *name" "FILE *stream" "unsigned int versions" \
   "unsigned long max_size"
Pp
Fn log_new_null_channel
Pp
The functions
Fn log_inc_references
and
Fn log_dec_references
increment or decrements, respectively, the
Va references
field of the logging channel pointed to by
Dq Fa chan ,
if it is a valid channel (and if the
Va references
field is strictly positive, in the case of
Fn log_dec_references ) .
These functions are meant to track changes in the number of different clients
which refer to the given logging channel.
Pp
The
Fn log_free_channel
function frees the
field of the logging channel pointed to by
Dq Fa chan
if there are no more outstanding references to it.  If the channel uses a file,
the stream is
Xr fclose 3 Ns -d
(if the
Dv LOG_CLOSE_STREAM
flag is set), and the filename, if
No non- Ns Dv NULL ,
is
Xr free 3 Ns -d
before
Dq Fa chan
is
Xr free 3 Ns -d .
Pp
\" The following requests should be uncommented and
\" used where appropriate.  This next request is
\" for sections 2 and 3 function return values only.
Sh RETURN VALUES
\" This next request is for sections 1, 6, 7 & 8 only
Bl -tag -width "log_category_is_active()"
It Fn log_open_stream
Dv NULL
is returned under any of several error conditions:
a) if
Dq Fa chan
is either
Dv NULL
or a
No non- Ns Dv log_file
channel
Pq Va errno No is set to Dv EINVAL ;
b) if either versioning or truncation is requested for a non-normal file
Pq Va errno No is set to Dv EINVAL ;
c) if any of
Xr stat 2 ,
Xr open 2 ,
or
Xr fdopen 3
fails
Po
Va errno
is set by the call which failed
Pc .
If some value other than
Dv NULL
is returned, then it is a valid logging stream (either newly-opened or
already-open).
It Fn log_close_stream
-1 if the stream associated with
Dq Fa chan
is
No non- Ns Dv NULL
and the call to
Xr fclose 3
fails.
0 if successful or the logging channel pointed to by
Dq Fa chan
is invalid (i.e.,
Dv NULL
or not a logging channel which has uses a file); in the latter case,
Va errno
is set to
Dv EINVAL .
It Fn log_get_stream
Dv NULL
under the same conditions as those under which
Fn log_close_stream ,
above, returns 0 (including the setting of
Va errno ) .
Otherwise, the stream associated with the logging channel is returned.
It Fn log_get_filename
Dv NULL
under the same conditions as those under which
Fn log_close_stream ,
above, returns 0 (including the setting of
Va errno ) .
Otherwise, the name of the file associated with the logging channel is
returned.
It Fn log_new_context
-1 if
Xr malloc 3
fails
Pq with Va errno No set to Dv ENOMEM .
Otherwise, 0, with
Dq Va lc->opaque
containing the new structures and information.
It Fn log_add_channel
-1 if
a) either
Dq Va lc.opaque
is
Dv NULL
or
Fa category
is invalid (negative or greater than or equal to
Va lcp->num_categories ) ,
with
Va errno
set to
Dv EINVAL ;
b)
Xr malloc 3
fails
Pq with Va errno No set to Dv ENOMEM .
Otherwise, 0.
It Fn log_remove_channel
-1 if
a) either
Dq Va lc.opaque
is
Dv NULL
or
Fa category
is invalid, as under failure condition a) for
Fn log_add_channel ,
above, including the setting of
Va errno ;
b) no channel numbered
Fa chan
is found in the logging context indicated by
Fa lc
Pq with Va errno No set to Dv ENOENT .
Otherwise, 0.
It Fn log_option
-1 if
a)
Dq Va lc.opaque
is
Dv NULL ,
b)
Fa option
specifies an unknown logging option;
in either case,
Va errno
is set to
Dv EINVAL .
Otherwise, 0.
It Fn log_category_is_active
-1 if
Dq Va lc.opaque
is
Dv NULL
Pq with Va errno No set to Dv EINVAL ;
1 if the
Fa category
number is valid and there are logging channels in this
Fa category
within the indicated logging context; 0 if the
Fa category
number is invalid or there are no logging channels in this
Fa category
within the indicated logging context.
It Fn log_new_syslog_channel
Dv NULL
if
Xr malloc 3
fails
Pq with Va errno No set to ENOMEM ;
otherwise, a valid
Dv log_syslog Ns -type
Ft log_channel .
It Fn log_new_file_channel
Dv NULL
if
Xr malloc 3
fails
Pq with Va errno No set to ENOMEM ;
otherwise, a valid
Dv log_file Ns -type
Ft log_channel .
It Fn log_new_null_channel
Dv NULL
if
Xr malloc 3
fails
Pq with Va errno No set to ENOMEM ;
otherwise, a valid
Dv log_null Ns -type
Ft log_channel .
It Fn log_inc_references
-1 if
Dq Fa chan
is
Dv NULL
Pq with Va errno set to Dv EINVAL .
Otherwise, 0.
It Fn log_dec_references
-1 if
Dq Fa chan
is
Dv NULL
or its
Va references
field is already <= 0
Pq with Va errno set to Dv EINVAL .
Otherwise, 0.
It Fn log_free_channel
-1 under the same conditions as
Fn log_dec_references ,
above, including the setting of
Va errno ;
0 otherwise.
El
\" .Sh ENVIRONMENT
Sh FILES
Bl -tag -width "isc/logging.h"
It Pa isc/logging.h
include file for logging library
It Pa syslog.h
Xr syslog 3 Ns -style
priorities
El
\" .Sh EXAMPLES
\" This next request is for sections 1, 6, 7 & 8 only
\"     (command return values (to shell) and
\"    fprintf/stderr type diagnostics)
\" .Sh DIAGNOSTICS
\" The next request is for sections 2 and 3 error
\" and signal handling only.
Sh ERRORS
This table shows which functions can return the indicated error in the
Va errno
variable; see the
Sx RETURN VALUES
section, above, for more information.
Bl -tag -width "(any0other0value)0"
It Dv EINVAL
Fn log_open_stream ,
Fn log_close_stream ,
Fn log_get_stream ,
Fn log_get_filename ,
Fn log_add_channel ,
Fn log_remove_channel ,
Fn log_option ,
Fn log_category_is_active ,
Fn log_inc_references ,
Fn log_dec_references ,
Fn log_free_channel .
It Dv ENOENT
Fn log_remove_channel .
It Dv ENOMEM
Fn log_new_context ,
Fn log_add_channel ,
Fn log_new_syslog_channel ,
Fn log_new_file_channel ,
Fn log_new_null_channel .
It (any other value)
returned via a pass-through of an error code from
Xr stat 2 ,
Xr open 2 ,
or
Xr fdopen 3 ,
which can occur in
Fn log_open_stream
and functions which call it
Pq currently, only Fn log_vwrite .
El
Pp
Additionally,
Fn log_vwrite
and
Fn log_free_context
will fail via
Fn assert
if
Dq Va lc.opaque
is
Dv NULL .
The function
Fn log_vwrite
can also exit with a critical error logged via
Xr syslog 3
indicating a memory overrun
Sh SEE ALSO
Xr @INDOT@named @SYS_OPS_EXT@ ,
Xr syslog 3 .
The HTML documentation includes a file,
Pa logging.html ,
which has more information about this logging system.
\" .Sh STANDARDS
\" .Sh HISTORY
Sh AUTHORS
Bob Halley...TODO
\" .Sh BUGS

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