stat

stat() retrieve information about the file pointed to by pathname;

lstat

lstat() is identical to stat(), except that if pathname is a symbolic link, then it returns information about the link itself, not the file that the link refers to.

fstat

stat() is identical to stat(), except that the file about which information is to be retrieved is specified by the file descriptor fd.

fstat and stat

If “stat()” could return the information about the file too, why we still need to first call “open()” to make a FD then use fstat?

The main reason is security, if you first “stat()” the file and then “open()” it, there is a small window of time in between where the file could have been modified or had its permissions changed, or replaced by a symlink. You can understand its a READ but not EXCLUSIVE operation.

“fstat()” make it OK in this scence. Because if you call “open()” first, then the file can not change by other process now.