"No manual entry for pthread" - could not find man page by name

First install these manpages:

sudo apt-get install manpages-posix manpages-posix-dev

and then:

man pthreads

Now it should work.

Ok, so the man page you look for is not there:

$ man pthread
No manual entry for pthread

Hmm... let's look for something similar!
We will se man option -k for that:

$ man -k pthread 
pthread_attr_destroy (3) - initialize and destroy thread attributes object
pthread_attr_getaffinity_np (3) - set/get CPU affinity attribute in thread attributes object
pthread_attr_getdetachstate (3) - set/get detach state attribute in thread attributes object
pthread_attr_getguardsize (3) - set/get guard size attribute in thread attributes object
[... 47 more lines ...]
pthread_timedjoin_np (3) - try to join with a terminated thread
pthread_tryjoin_np (3) - try to join with a terminated thread
pthread_yield (3)    - yield the processor
pthreads (7)         - POSIX threads
vfs_aio_pthread (8)  - implement async I/O in Samba vfs using a pthread pool

Ok... some related stuff... Oh! pthreads looks interesting!

$ man pthreads|head -n 12
PTHREADS(7)           Linux Programmer's Manual          PTHREADS(7)



NAME
       pthreads - POSIX threads

DESCRIPTION
       POSIX.1  specifies  a  set  of  interfaces (functions, header
       files) for  threaded  programming  commonly  known  as  POSIX
       threads,  or Pthreads.  A single process can contain multiple
       threads, all of which are executing the same program.   These

Now, looks like we found it!