python - What does this daemonize method do? -


i looking around on github, when stumbled across method called daemonize() in reverse shell example. source

what don't quite understand in context, wouldn't running code command line such: python example.py & not achieve same thing?

deamonize method source:

def daemonize():     pid = os.fork()     if pid > 0:         sys.exit(0)   # exit first parent     pid = os.fork()     if pid > 0:         sys.exit(0)   # exit second parent

a background process - running python2.7 <file>.py & signal - not same thing true daemon process.

a true daemon process:

  • runs in background. happens if use &, , similarity ends.
  • is not in same process group terminal. when terminal closes, daemon not die either. not happen & - process remains same, moved background.
  • properly closes inherited file descriptors (including input, output, etc.) nothing ties parent. again, not happen & - still write terminal.
  • should ideally killed sigkill, not sighup. running & allows process killed sighup.

all of this, however, pedantry. few tasks require go extreme these properties require - background task spawned in new terminal using screen can same job, though less efficiently, , may call daemon in long-running background task. real difference between that , true daemon latter tries avoid avenues of potential death.

the code saw forks current process. essentially, clones current process, kills parent , 'acts in background' being separate process not block current execution - bit of ugly hack, if ask me, works.


Comments

Post a Comment

Popular posts from this blog

jOOQ update returning clause with Oracle -

according http://www.jooq.org/doc/3.8/manual/sql-building/sql-statements/update-statement/ jooq doesn't support returning clause in update statements databases except firebird , postgres. does know, still correct oracle jooq? according oracle's documentation, oracle db supports returning clase delete, insert, or update statements. incorrect manual you're right - manual wrong , should fixed: https://github.com/jooq/jooq/issues/5470 single row update returning jooq 3.8 added support single row update .. returning statements. internally, uses callablestatement , pl/sql block of form: begin update "my_table" set "my_table"."column" = 'xyz' "my_table"."id" = 1 returning "my_table"."id", "my_table"."column" ?, ?; ? := sql%rowcount; end; the relevant issue is: https://github.com/jooq/jooq/issues/5190 multi row update returning a...
Read more

java - Warning equals/hashCode on @Data annotation lombok with inheritance -

i have entity inherits other. on other hand, i'm using lombok project reduce boilerplate code, put @data annotation. annotation @data inheritance produces next warning: generating equals/hashcode implementation without call superclass, though class not extend java.lang.object. if intentional, add '@equalsandhashcode(callsuper=false)' type. is advisable add annotation @equalsandhashcode (callsuper = true) or @equalsandhashcode (callsuper = false) ? if not added, 1 callsuper=false or callsuper=true ? the default value false . 1 if don't specify , ignore warning. yes, recommended add @equalsandhashcode annotation on @data annotated classes extend else object. cannot tell if need true or false , depends on class hierarchy, , need examined on case-by-case basis. however, project or package, can configure in lombok.config call super methods if not direct subclass of object. lombok.equalsandhashcode.callsuper = call for configuration system ...
Read more

java - BasicPathUsageException: Cannot join to attribute of basic type -

i using java 8 jpa (hibernate 5.2.1). have clause works perfectly, until introduce clause make use foreign key table values too. i getting following error: basicpathusageexception: cannot join attribute of basic type i think problem related fact have join table, , not sure how create join using join table. employee - employee_category - category model (employee.java): @manytomany(cascade = cascadetype.all, fetch=fetchtype.eager) @jointable ( name="employee_category", joincolumns={ @joincolumn(name="emp_id", referencedcolumnname="id") }, inversejoincolumns={ @joincolumn(name="cat_id", referencedcolumnname="id") } ) private set<category> categories; model (category.java): @id private string id; jpa when introduce following code, fails error above (i think problem new piece of code): join<t, category> category = from.join("id"); predicates.add(criteriabuilder.like(category....
Read more