Envoyé par man
DESCRIPTION
Apply, test or remove a POSIX lock on a section of an open file. The
file is specified by fd, a file descriptor open for writing, the action
by cmd, and the section consists of byte positions pos..pos+len-1 if
len is positive, and pos-len..pos-1 if len is negative, where pos is
the current file position, and if len is zero, the section extends from
the current file position to infinity, encompassing the present and
future end-of-file positions. In all cases, the section may extend
past current end-of-file.
