gyz@debian:~$ man  pthread_mutex_lock
No manual entry for pthread_mutex_lock
gyz@debian:~$ sudo apt-get install manpages-posix-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package manpages-posix-dev
gyz@debian:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 10 (buster)
Release:        10
Codename:       buster
gyz@debian:~$ getconf LONG_BIT
64
gyz@debian:~$ cat /proc/version
Linux version 4.19.0-9-amd64 (debian-kernel@lists.debian.org) (gcc version 8.3.0 (Debian 8.3.0-6)) #1 
SMP Debian 4.19.118-2+deb10u1 (2020-06-07)

manpages-posix manpages-posix-dev

gyz@debian:~$ sudo apt-get install glibc-doc