4 \section*{Python Scripting}
5 \label{_ChapterStart60}
6 \index[general]{Python Scripting}
7 \index[general]{Scripting!Python}
8 \addcontentsline{toc}{section}{Python Scripting}
10 You may be asking what Python is and why a scripting language is
11 needed in Bacula. The answer to the first question is that Python
12 is an Object Oriented scripting language with features similar
13 to those found in Perl, but the syntax of the language is much
14 cleaner and simpler. The answer to why have scripting in Bacula is to
15 give the user more control over the whole backup process. Probably
16 the simplest example is when Bacula needs a new Volume name, with
17 a scripting language such as Python, you can generate any name
18 you want, based on the current state of Bacula.
20 \subsection*{Python Configuration}
21 \index[general]{Python Configuration}
22 \index[general]{Configuration!Python}
23 \addcontentsline{toc}{subsection}{Python Configuration}
25 Python must be enabled during the configuration process by adding
26 a \verb:--:with-python, and possibly specifying an alternate
27 directory if your Python is not installed in a standard system
28 location. If you are using RPMs you will need the python-devel package
31 When Python is configured, it becomes an integral part of Bacula and
32 runs in Bacula's address space, so even though it is an interpreted
33 language, it is very efficient.
35 When the Director starts, it looks to see if you have a {\bf
36 Scripts Directory} Directive defined, if so, it looks in that directory for
37 a file named {\bf DirStartUp.py}. If it is found, Bacula will pass this
38 file to Python for execution. The {\bf Scripts Directory} is a new
39 directive that you add to the Director resource of your bacula-dir.conf
42 \subsection*{Bacula Events}
43 \index[general]{Bacula Events}
44 \index[general]{Events}
45 \addcontentsline{toc}{subsection}{Bacula Events}
46 A Bacula event is a point in the Bacula code where Bacula
47 will call a subroutine (actually a method) that you have
48 defined in the Python StartUp script. Events correspond
49 to some significant event such as a Job Start, a Job End,
50 Bacula needs a new Volume Name, ... When your script is
51 called, it will have access to all the Bacula variables
52 specific to the Job (attributes of the Job Object), and
53 it can even call some of the Job methods (subroutines)
54 or set new values in the Job attributes, such as the
55 Priority. You will see below how the events are used.
57 \subsection*{Python Objects}
58 \index[general]{Python Objects}
59 \index[general]{Objects!Python}
60 \addcontentsline{toc}{subsection}{Python Objects}
62 There are four Python objects that you will need to work with:
64 \item [The Bacula Object]
65 The Bacula object is created by the Bacula daemon (the Director
66 in the present case) when the daemon starts. It is available to
67 the Python startup script, {\bf DirStartup.py}, by importing the
68 Bacula definitions with {\bf import bacula}. The methods
69 available with this object are described below.
71 \item [The Bacula Events Class]
72 You create this class in the startup script, and you pass
73 it to the Bacula Object's {\bf set\_events} method. The
74 purpose of the Bacula Events Class is to define what global
75 or daemon events you want to monitor. When one of those events
76 occurs, your Bacula Events Class will be called at the method
77 corresponding to the event. There are currently three events,
78 JobStart, JobEnd, and Exit, which are described in detail below.
80 \item [The Job Object]
81 When a Job starts, and assuming you have defined a JobStart method
82 in your Bacula Events Class, Bacula will create a Job Object. This
83 object will be passed to the JobStart event. The Job Object has a
84 has good number of read-only members or attributes providing many
85 details of the Job, and it also has a number of writable attributes
86 that allow you to pass information into the Job. These attributes
89 \item [The Job Events Class]
90 You create this class in the JobStart method of your Bacula Events
91 class, and it allows you to define which of the possible Job Object
92 events you want to see. You must pass an instance of your Job Events
93 class to the Job Object set\_events() method.
94 Normally, you will probably only have one
95 Job Events Class, which will be instantiated for each Job. However,
96 if you wish to see different events in different Jobs, you may have
97 as many Job Events classes as you wish.
101 The first thing the startup script must do is to define what global Bacula
102 events (daemon events), it wants to see. This is done by creating a
103 Bacula Events class, instantiating it, then passing it to the
104 {\bf set\_events} method. There are three possible
109 \index[dir]{JobStart}
110 This Python method, if defined, will be called each time a Job is started.
111 The method is passed the class instantiation object as the first argument,
112 and the Bacula Job object as the second argument. The Bacula Job object
113 has several built-in methods, and you can define which ones you
114 want called. If you do not define this method, you will not be able
115 to interact with Bacula jobs.
118 This Python method, if defined, will be called each time a Job terminates.
119 The method is passed the class instantiation object as the first argument,
120 and the Bacula Job object as the second argument.
123 This Python method, if defined, will be called when the Director terminates.
124 The method is passed the class instantiation object as the first argument.
127 Access to the Bacula variables and methods is done with:
131 The following are the read-only attributes provided by the bacula object.
136 \item [Version] string consisting of "Version Build-date"
140 A simple definition of the Bacula Events Class might be the following:
146 def JobStart(self, job):
151 Then to instantiate the class and pass it to Bacula, you
156 bacula.set_events(BaculaEvents()) # register Bacula Events wanted
160 And at that point, each time a Job is started, your BaculaEvents JobStart
161 method will be called.
163 Now to actually do anything with a Job, you must define which Job events
164 you want to see, and this is done by defining a JobEvents class containing
165 the methods you want called. Each method name corresponds to one of the
166 Job Events that Bacula will generate.
168 A simple Job Events class might look like the following:
173 def NewVolume(self, job):
178 Here, your JobEvents class method NewVolume will be called each time
179 the Job needs a new Volume name. To actually register the events defined
180 in your class with the Job, you must instantiate the JobEvents class and
181 set it in the Job {\bf set\_events} variable. Note, this is a bit different
182 from how you registered the Bacula events. The registration process must
183 be done in the Bacula JobStart event (your method). So, you would modify
184 Bacula Events (not the Job events) as follows:
190 def JobStart(self, job):
191 events = JobEvents() # create instance of Job class
192 job.set_events(events) # register Job events desired
197 When a job event is triggered, the appropriate event definition is
198 called in the JobEvents class. This is the means by which your Python
199 script or code gets control. Once it has control, it may read job
200 attributes, or set them. See below for a list of read-only attributes,
201 and those that are writable.
203 In addition, the Bacula {\bf job} obbject in the Director has
204 a number of methods (subroutines) that can be called. They
207 \item [set\_events] The set\_events method takes a single
208 argument, which is the instantation of the Job Events class
209 that contains the methods that you want called. The method
210 names that will be called must correspond to the Bacula
211 defined events. You may define additional methods but Bacula
213 \item [run] The run method takes a single string
214 argument, which is the run command (same as in the Console)
215 that you want to submit to start a new Job. The value
216 returned by the run method is the JobId of the job that
217 started, or -1 if there was an error.
218 \item [write] The write method is used to be able to send
219 print output to the Job Report. This will be described later.
220 \item[cancel] The cancel method takes a single integer argument,
221 which is a JobId. If JobId is found, it will be canceled.
222 \item [DoesVolumeExist] The DoesVolumeExist method takes a single
223 string argument, which is the Volume name, and returns
224 1 if the volume exists in the Catalog and 0 if the volume
228 The following attributes are read/write within the Director
229 for the {\bf job} object.
232 \item [Priority] Read or set the Job priority.
233 Note, that setting a Job Priority is effective only before
234 the Job actually starts.
235 \item [Level] This attribute contains a string representing the Job
236 level, e.g. Full, Differential, Incremental, ... if read.
237 The level can also be set.
240 The following read-only attributes are available within the Director
241 for the {\bf job} object.
245 \item [Type] This attribute contains a string representing the Job
246 type, e.g. Backup, Restore, Verify, ...
247 \item [JobId] This attribute contains an integer representing the
249 \item [Client] This attribute contains a string with the name of the
251 \item [NumVols] This attribute contains an integer with the number of
252 Volumes in the Pool being used by the Job.
253 \item [Pool] This attribute contains a string with the name of the Pool
254 being used by the Job.
255 \item [Storage] This attribute contains a string with the name of the
256 Storage resource being used by the Job.
257 \item [Catalog] This attribute contains a string with the name of the
258 Catalog resource being used by the Job.
259 \item [MediaType] This attribute contains a string with the name of the
260 Media Type associated with the Storage resource being used by the Job.
261 \item [Job] This attribute contains a string containing the name of the
262 Job resource used by this job (not unique).
263 \item [JobName] This attribute contains a string representing the full
265 \item [JobStatus] This attribute contains a single character string
266 representing the current Job status. The status may change
267 during execution of the job.
268 \item [Priority] This attribute contains an integer with the priority
270 \item [CatalogRes] tuple consisting of (DBName, Address, User,
271 Password, Socket, Port, Database Vendor) taken from the Catalog resource
272 for the Job with the exception of Database Vendor, which is
273 one of the following: MySQL, PostgreSQL, SQLite, Internal,
274 depending on what database you configured.
276 After a Volume has been purged, this attribute will contain the
277 name of that Volume. At other times, this value may have no meaning.
280 The following write-only attributes are available within the
284 \item [JobReport] Send line to the Job Report.
285 \item [VolumeName] Set a new Volume name. Valid only during the
289 \subsection*{Python Console Command}
290 \index[general]{Python Console Command}
291 \index[general]{Console Command!Python}
292 \addcontentsline{toc}{subsection}{Python Console Command}
294 There is a new Console command named {\bf python}. It takes
295 a single argument {\bf restart}. Example:
300 This command restarts the Python interpreter in the Director.
301 This can be useful when you are modifying the DirStartUp script,
302 because normally Python will cache it, and thus the
303 script will be read one time.
306 \subsection*{Python Example}
307 \index[general]{Python Example}
308 \index[general]{Example!Python}
309 \addcontentsline{toc}{subsection}{Python Example}
311 An example script for the Director startup file is provided in
312 {\bf examples/python/DirStartup.py} as follows:
317 # Bacula Python interface script for the Director
320 # You must import both sys and bacula
323 # This is the list of Bacula daemon events that you
327 # Called here when a new Bacula Events class is
328 # is created. Normally not used
331 def JobStart(self, job):
333 Called here when a new job is started. If you want
334 to do anything with the Job, you must register
335 events you want to receive.
337 events = JobEvents() # create instance of Job class
338 events.job = job # save Bacula's job pointer
339 job.set_events(events) # register events desired
340 sys.stderr = events # send error output to Bacula
341 sys.stdout = events # send stdout to Bacula
342 jobid = job.JobId; client = job.Client
343 numvols = job.NumVols
344 job.JobReport="Python Dir JobStart: JobId=%d Client=%s NumVols=%d\n" % (jobid,client,numvols)
346 # Bacula Job is going to terminate
347 def JobEnd(self, job):
350 job.JobReport="Python Dir JobEnd output: JobId=%d Client=%s.\n" % (jobid, client)
352 # Called here when the Bacula daemon is going to exit
354 print "Daemon exiting."
356 bacula.set_events(BaculaEvents()) # register daemon events desired
359 These are the Job events that you can receive.
363 # Called here when you instantiate the Job. Not
368 # Called when the job is first scheduled
372 # Called just before running the job after initializing
373 # This is the point to change most Job parameters.
374 # It is equivalent to the JobRunBefore point.
377 def NewVolume(self, job):
378 # Called when Bacula wants a new Volume name. The Volume
379 # name returned, if any, must be stored in job.VolumeName
383 volname = "TestA-001"
384 job.JobReport = "JobId=%d Client=%s NumVols=%d VolumeName=%s" % (jobid, client, numvol,volname)
385 job.JobReport="Python before New Volume set for Job.\n"
386 job.VolumeName=volname
388 def VolumePurged(self, job):
389 # Called when a Volume is purged. The Volume name can be referenced
390 # with job.VolumeName