inotify monitor doesn't detect fast file creation recursively

[gbroques]

Hi, it doesn't seem like the inotify monitor properly detects file creation recursively.

I'm using this to detect changes to the .git/ directory.

The following are steps to reproduce (using bash as a terminal):

mkdir test
cd test
git init
fswatch -rx .git/
echo "one" > 1.txt
git add 1.txt

I see the following directory is created:

/path/to/test/.git/objects/56 Created

However, I would expect to see the object file itself being created:

# Missing ❌👇
/path/to/test/.git/objects/56/26abf0f72e58d7a153368ba57db4c673c0e171

I tested using version 1.14.0.

---

As an aside, inotifywait correctly detects this:

inotifywait -m .git/ -r

Then you see the following output:

.git/objects/56/ CREATE 26abf0f72e58d7a153368ba57db4c673c0e171

However, it's my understanding that inotifywait has additional code on top of inotify for recursive watching.

[emcrisostomo]

Hey @gbroques, thanks for opening this one.

Actually, from the perspective of inotify and the linux kernel, that's exactly what happens: inotify doesn't give you information about file creation "recursively" down a hierarchy, it only gives information about files created into a directory that is being watched using inotify.

Now: even if you quickly setup a new watch on a subdirectory that has been created into a watched directory, there's a race condition and you might miss file creations that happen inside that subtree. That was a problem with inotifywait as well. What they ended up doing is firing "synthetic" creation events in that circumstance. More details here:

inotify-tools/inotify-tools#121

When I designed fswatch I was looking at it from the perspective of the various OS APIs it has and decided to respect their semantics. In the case of kqueue, for example, it's even worse: you don't even get the name of a created file inside a watched directory.

But years have passed and a lot of people rely on fswatch for workloads where it doesn't make sense to ask them to rescan a subtree. I'm opening a branch to fix this once and for all.

[gbroques]

Hey @gbroques, thanks for opening this one.

Actually, from the perspective of inotify and the linux kernel, that's exactly what happens: inotify doesn't give you information about file creation "recursively" down a hierarchy, it only gives information about files created into a directory that is being watched using inotify.

Now: even if you quickly setup a new watch on a subdirectory that has been created into a watched directory, there's a race condition and you might miss file creations that happen inside that subtree. That was a problem with inotifywait as well. What they ended up doing is firing "synthetic" creation events in that circumstance. More details here:

inotify-tools/inotify-tools#121

When I designed fswatch I was looking at it from the perspective of the various OS APIs it has and decided to respect their semantics. In the case of kqueue, for example, it's even worse: you don't even get the name of a created file inside a watched directory.

But years have passed and a lot of people rely on fswatch for workloads where it doesn't make sense to ask them to rescan a subtree. I'm opening a branch to fix this once and for all.

Thank you for sharing those insights and thoughts @emcrisostomo!

I really appreciate the fast response.

If it's at all helpful, both dmon and efsw detect recursive file creation in this example as well somehow.

Looking forward to this enhancement!

[emcrisostomo]

If you want to try this branch version I'm attaching a source tarball for your convenience to build locally (./configure && make && make install).

I'll try this out more in the next few days and prepare a release.

fswatch-1.19.0-alpha.tar.gz

[gbroques]

If you want to try this branch version I'm attaching a source tarball for your convenience to build locally (./configure && make && make install).

I'll try this out more in the next few days and prepare a release.

fswatch-1.19.0-alpha.tar.gz

Ok, I may try it it if I find time. Thank you! It's been several years since I've programmed C++ back in university, and I'm just getting back into it for this project since it seems like C/C++ is the way to go for filesystem monitoring.

You had mentioned there's a race condition where you might miss file creation in a newly created subtree of a watched directory if you don't establish the new watch fast enough.

Does inotify-wait's "synthetic event" approach make that full-proof, or just less brittle?

I had migrated to efsw and it seems to work sometimes, and not other times.

If it's not full-proof, then I might consider a polling strategy or some other approach to ensure I don't miss events.

[emcrisostomo]

Hey! You won't need any GNU build system nor C++ knowledge to build that source tarball: that's the point of it, stripping dependencies from the user, it's just a ./configure && make && make install.

To your question: the race condition is due to how inotify works: it doesn't watch subdirectories of a watched directory. This is very different with how fsevents work on macOS, which indeed provides you that guarantee.

My approach in fswatch is this:

• A creation of a subdirectory in a watched directory is detected (no races, deterministic).
• A new watch on that directory is set to be registered as soon as possible.
• As soon as the watch is registered, events are guaranteed to be delivered.
• As soon as the watch is registered, the subdirectory is scanned and a new synthetic creation event is triggered for each object in it.

The potential for a race is now just a vanishing file that's being created and deleted between the directory creation and the new watch being setup.

If your question is limited to files that do not vanish that way, then you should be perfectly fine.

[gbroques]

Hey! You won't need any GNU build system nor C++ knowledge to build that source tarball: that's the point of it, stripping dependencies from the user, it's just a ./configure && make && make install.

To your question: the race condition is due to how inotify works: it doesn't watch subdirectories of a watched directory. This is very different with how fsevents work on macOS, which indeed provides you that guarantee.

My approach in fswatch is this:

• A creation of a subdirectory in a watched directory is detected (no races, deterministic).
• A new watch on that directory is set to be registered as soon as possible.
• As soon as the watch is registered, events are guaranteed to be delivered.
• As soon as the watch is registered, the subdirectory is scanned and a new synthetic creation event is triggered for each object in it.

The potential for a race is now just a vanishing file that's being created and deleted between the directory creation and the new watch being setup.

If your question is limited to files that do not vanish that way, then you should be perfectly fine.

Thank you for that very clear explanation — makes sense!

I think for my use-case, then I should be good as I don't need to detect any fast recrusive deletion followed by creation.

Would your approach potentially create duplicate file creation events in the case the watch was fast enough, and then you scan to emit a synthetic creation event, or are you somehow handling that too?

---

Also, I tried installing the tarball, but the fswatch executable fails to find the libfswatch.so.13 file.

$ fswatch ⏎
fswatch: error while loading shared libraries: libfswatch.so.13: cannot open shared object file: No such file or directory

That file exists in /usr/local/lib so I'm not sure what went wrong:

$ ls /usr/local/lib ⏎
libfswatch.a    libfswatch.so.13@      python3.10/
libfswatch.la*  libfswatch.so.13.0.1*
libfswatch.so@  pkgconfig/

Below is the output from the installation command, and it failed with a "Permission denied", so I re-ran make install and make with sudo:

~/Downloads/fswatch-1.19.0-alpha $ ./configure && make && make install ⏎
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking target system type... x86_64-pc-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
checking whether sleep supports fractional seconds... yes
checking filesystem timestamp resolution... 0.01
checking whether build environment is sane... yes
checking for a race-free mkdir -p... /usr/bin/mkdir -p
checking for gawk... no
checking for mawk... mawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking xargs -n works... yes
checking whether make supports the include directive... yes (GNU style)
checking for gcc... gcc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether the compiler supports GNU C... yes
checking whether gcc accepts -g... yes
checking for gcc option to enable C11 features... none needed
checking whether gcc understands -c and -o together... yes
checking dependency style of gcc... gcc3
checking for ar... ar
checking the archiver (ar) interface... ar
checking for clang++... no
checking for g++... g++
checking whether the compiler supports GNU C++... yes
checking whether g++ accepts -g... yes
checking for g++ option to enable C++11 features... none needed
checking dependency style of g++... gcc3
checking how to print strings... printf
checking for a sed that does not truncate output... /usr/bin/sed
checking for grep that handles long lines and -e... /usr/bin/grep
checking for egrep... /usr/bin/grep -E
checking for fgrep... /usr/bin/grep -F
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking whether ln -s works... yes
checking the maximum length of command line arguments... 1572864
checking how to convert x86_64-pc-linux-gnu file names to x86_64-pc-linux-gnu format... func_convert_file_noop
checking how to convert x86_64-pc-linux-gnu file names to toolchain format... func_convert_file_noop
checking for /usr/bin/ld option to reload object files... -r
checking for file... file
checking for objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for dlltool... no
checking how to associate runtime and link libraries... printf %s\n
checking for ranlib... ranlib
checking for archiver @FILE support... @
checking for strip... strip
checking command to parse /usr/bin/nm -B output from gcc object... ok
checking for sysroot... no
checking for a working dd... /usr/bin/dd
checking how to truncate binary pipes... /usr/bin/dd bs=4096 count=1
checking for mt... mt
checking if mt is a manifest tool... no
checking for stdio.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for strings.h... yes
checking for sys/stat.h... yes
checking for sys/types.h... yes
checking for unistd.h... yes
checking for dlfcn.h... yes
checking for objdir... .libs
checking if gcc supports -fno-rtti -fno-exceptions... no
checking for gcc option to produce PIC... -fPIC -DPIC
checking if gcc PIC flag -fPIC -DPIC works... yes
checking if gcc static flag -static works... yes
checking if gcc supports -c -o file.o... yes
checking if gcc supports -c -o file.o... (cached) yes
checking whether the gcc linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
checking how to run the C++ preprocessor... g++ -E
checking for ld used by g++... /usr/bin/ld -m elf_x86_64
checking if the linker (/usr/bin/ld -m elf_x86_64) is GNU ld... yes
checking whether the g++ linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking for g++ option to produce PIC... -fPIC -DPIC
checking if g++ PIC flag -fPIC -DPIC works... yes
checking if g++ static flag -static works... yes
checking if g++ supports -c -o file.o... yes
checking if g++ supports -c -o file.o... (cached) yes
checking whether the g++ linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking dynamic linker characteristics... (cached) GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking for C++ compiler vendor... gnu
checking for C++ compiler version... 11.4.0
checking for doxygen... no
configure: WARNING: Doxygen support disabled
checking for makeinfo... /usr/bin/makeinfo
checking whether NLS is requested... yes
checking for msgfmt... no
checking for gmsgfmt... :
checking for xgettext... no
checking for msgmerge... no
checking for ld... /usr/bin/ld -m elf_x86_64
checking if the linker (/usr/bin/ld -m elf_x86_64) is GNU ld... yes
checking for shared library run path origin... done
checking 32-bit host C ABI... no
checking for egrep -e... (cached) /usr/bin/grep -E
checking for ELF binary format... yes
checking for the common suffixes of directories in the library search path... lib,lib,lib64
checking for CFPreferencesCopyAppValue... no
checking for CFLocaleCopyPreferredLanguages... no
checking for GNU gettext in libc... yes
checking whether to use NLS... yes
checking where the gettext function comes from... libc
checking whether g++ supports C++17 features with -std=c++17... yes
checking CXXFLAGS for most reasonable warnings... -Wall
checking for getopt.h... yes
checking for sys/event.h... no
checking for g++ -std=c++17 options needed to detect all undeclared functions... none needed
checking for port.h... no
checking for sys/inotify.h... yes
checking whether inotify_init is declared... yes
checking whether inotify_add_watch is declared... yes
checking whether inotify_rm_watch is declared... yes
checking for inotify_init in -lc... yes
checking for windows.h... no
checking for struct stat.st_mtime... yes
checking for struct stat.st_mtimespec... no
checking whether lstat correctly handles trailing slash... yes
checking for getopt_long... yes
checking for git... /usr/bin/git
checking for current git branch... fatal: not a git repository (or any of the parent directories): .git

configure: WARNING: An error occurred while invoking git
checking for GNU date... yes
checking for BSD date... no
checking for date type... gnu
checking whether GNU date supports --date... yes
checking whether GNU date supports --utc... yes
checking that generated files are newer than configure... done
configure: creating ./config.status
config.status: creating Makefile
config.status: creating libfswatch/Makefile
config.status: creating libfswatch/doc/doxygen/Makefile
config.status: creating libfswatch/src/Makefile
config.status: creating libfswatch/src/libfswatch.pc
config.status: creating fswatch/Makefile
config.status: creating fswatch/src/Makefile
config.status: creating fswatch/doc/Makefile
config.status: creating po/Makefile.in
config.status: creating man/fswatch.7
config.status: creating libfswatch/libfswatch_config.h
config.status: executing depfiles commands
config.status: executing libtool commands
config.status: executing po-directories commands
config.status: creating po/POTFILES
config.status: creating po/Makefile
Making all in libfswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make  all-recursive
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making all in src
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
  CXX      libfswatch/c/cevent.lo
  CXX      libfswatch/c/libfswatch.lo
  CXX      libfswatch/c/libfswatch_log.lo
  CXX      libfswatch/c++/libfswatch_exception.lo
  CXX      libfswatch/c++/event.lo
  CXX      libfswatch/c++/filter.lo
  CXX      libfswatch/c++/monitor.lo
  CXX      libfswatch/c++/monitor_factory.lo
  CXX      libfswatch/c++/poll_monitor.lo
  CXX      libfswatch/c++/path_utils.lo
  CXX      libfswatch/c++/string/string_utils.lo
  CXX      libfswatch/c++/inotify_monitor.lo
  CXXLD    libfswatch.la
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
Making all in doc/doxygen
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[3]: Nothing to be done for 'all'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making all in fswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
Making all in src
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
  CXX      fswatch-fswatch.o
  CXXLD    fswatch
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
Making all in doc
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[2]: Nothing to be done for 'all'.
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[2]: Nothing to be done for 'all-am'.
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
Making all in po
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/po'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/po'
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha'
make[1]: Nothing to be done for 'all-am'.
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha'
Making install in libfswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making install in src
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
 /usr/bin/mkdir -p '/usr/local/lib'
 /bin/bash ../../libtool   --mode=install /usr/bin/install -c   libfswatch.la '/usr/local/lib'
libtool: install: /usr/bin/install -c .libs/libfswatch.so.13.0.1 /usr/local/lib/libfswatch.so.13.0.1
/usr/bin/install: cannot create regular file '/usr/local/lib/libfswatch.so.13.0.1': Permission denied
make[3]: *** [Makefile:602: install-libLTLIBRARIES] Error 1
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
make[2]: *** [Makefile:945: install-am] Error 2
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
make[1]: *** [Makefile:447: install-recursive] Error 1
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make: *** [Makefile:607: install-recursive] Error 1

That failed with a "Permission denied" error, so I ran sudo make install:

~/Downloads/fswatch-1.19.0-alpha $ sudo make install ⏎
[sudo] password for g: 
Making install in libfswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making install in src
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
 /usr/bin/mkdir -p '/usr/local/lib'
 /bin/bash ../../libtool   --mode=install /usr/bin/install -c   libfswatch.la '/usr/local/lib'
libtool: install: /usr/bin/install -c .libs/libfswatch.so.13.0.1 /usr/local/lib/libfswatch.so.13.0.1
libtool: install: (cd /usr/local/lib && { ln -s -f libfswatch.so.13.0.1 libfswatch.so.13 || { rm -f libfswatch.so.13 && ln -s libfswatch.so.13.0.1 libfswatch.so.13; }; })
libtool: install: (cd /usr/local/lib && { ln -s -f libfswatch.so.13.0.1 libfswatch.so || { rm -f libfswatch.so && ln -s libfswatch.so.13.0.1 libfswatch.so; }; })
libtool: install: /usr/bin/install -c .libs/libfswatch.lai /usr/local/lib/libfswatch.la
libtool: install: /usr/bin/install -c .libs/libfswatch.a /usr/local/lib/libfswatch.a
libtool: install: chmod 644 /usr/local/lib/libfswatch.a
libtool: install: ranlib /usr/local/lib/libfswatch.a
libtool: finish: PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin:/sbin" ldconfig -n /usr/local/lib
----------------------------------------------------------------------
Libraries have been installed in:
   /usr/local/lib

If you ever happen to want to link against installed libraries
in a given directory, LIBDIR, you must either use libtool, and
specify the full pathname of the library, or use the '-LLIBDIR'
flag during linking and do at least one of the following:
   - add LIBDIR to the 'LD_LIBRARY_PATH' environment variable
     during execution
   - add LIBDIR to the 'LD_RUN_PATH' environment variable
     during linking
   - use the '-Wl,-rpath -Wl,LIBDIR' linker flag
   - have your system administrator add LIBDIR to '/etc/ld.so.conf'

See any operating system documentation about shared libraries for
more information, such as the ld(1) and ld.so(8) manual pages.
----------------------------------------------------------------------
 /usr/bin/mkdir -p '/usr/local/include/libfswatch/c'
 /usr/bin/install -c -m 644 libfswatch/c/libfswatch.h libfswatch/c/libfswatch_types.h libfswatch/c/cevent.h libfswatch/c/cfilter.h libfswatch/c/cmonitor.h libfswatch/c/error.h libfswatch/c/libfswatch_log.h '/usr/local/include/libfswatch/c'
 /usr/bin/mkdir -p '/usr/local/include/libfswatch/c++'
 /usr/bin/install -c -m 644 libfswatch/c++/monitor.hpp libfswatch/c++/monitor_factory.hpp libfswatch/c++/path_utils.hpp libfswatch/c++/string/string_utils.hpp libfswatch/c++/inotify_monitor.hpp libfswatch/c++/poll_monitor.hpp libfswatch/c++/filter.hpp libfswatch/c++/event.hpp libfswatch/c++/libfswatch_exception.hpp '/usr/local/include/libfswatch/c++'
 /usr/bin/mkdir -p '/usr/local/lib/pkgconfig'
 /usr/bin/install -c -m 644 libfswatch.pc '/usr/local/lib/pkgconfig'
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
Making install in doc/doxygen
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[3]: Nothing to be done for 'install-exec-am'.
make[3]: Nothing to be done for 'install-data-am'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[3]: Nothing to be done for 'install-exec-am'.
make[3]: Nothing to be done for 'install-data-am'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making install in fswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
Making install in src
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
 /usr/bin/mkdir -p '/usr/local/bin'
  /bin/bash ../../libtool   --mode=install /usr/bin/install -c fswatch '/usr/local/bin'
libtool: install: /usr/bin/install -c .libs/fswatch /usr/local/bin/fswatch
make[3]: Nothing to be done for 'install-data-am'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
Making install in doc
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[3]: Nothing to be done for 'install-exec-am'.
 /usr/bin/mkdir -p '/usr/local/share/info'
 /usr/bin/install -c -m 644 ./fswatch.info '/usr/local/share/info'
 install-info --info-dir='/usr/local/share/info' '/usr/local/share/info/fswatch.info'
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[3]: Nothing to be done for 'install-exec-am'.
make[3]: Nothing to be done for 'install-data-am'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
Making install in po
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/po'
installing en.gmo as /usr/local/share/locale/en/LC_MESSAGES/fswatch.mo
installing en@quot.gmo as /usr/local/share/locale/en@quot/LC_MESSAGES/fswatch.mo
installing en@boldquot.gmo as /usr/local/share/locale/en@boldquot/LC_MESSAGES/fswatch.mo
installing it.gmo as /usr/local/share/locale/it/LC_MESSAGES/fswatch.mo
installing es.gmo as /usr/local/share/locale/es/LC_MESSAGES/fswatch.mo
if test "fswatch" = "gettext-tools"; then \
  /usr/bin/mkdir -p /usr/local/share/gettext/po; \
  for file in Makefile.in.in remove-potcdate.sin quot.sed boldquot.sed en@quot.header en@boldquot.header insert-header.sin Rules-quot   Makevars.template; do \
    /usr/bin/install -c -m 644 ./$file \
		    /usr/local/share/gettext/po/$file; \
  done; \
  for file in Makevars; do \
    rm -f /usr/local/share/gettext/po/$file; \
  done; \
else \
  : ; \
fi
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/po'
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha'
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha'
make[2]: Nothing to be done for 'install-exec-am'.
 /usr/bin/mkdir -p '/usr/local/share/doc/fswatch'
 /usr/bin/install -c -m 644 README.bsd README.codestyle README.freebsd README.gnu-build-system README.illumos README.md README.libfswatch.md README.linux README.macos README.smartos README.solaris README.windows ABOUT-NLS AUTHORS CONTRIBUTING.md COPYING NEWS AUTHORS.libfswatch NEWS.libfswatch '/usr/local/share/doc/fswatch'
 /usr/bin/mkdir -p '/usr/local/share/man/man7'
 /usr/bin/install -c -m 644 man/fswatch.7 '/usr/local/share/man/man7'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha'

~/Downloads/fswatch-1.19.0-alpha $ sudo make ⏎
Making all in libfswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make  all-recursive
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making all in src
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
make[3]: Nothing to be done for 'all'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/src'
Making all in doc/doxygen
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[3]: Nothing to be done for 'all'.
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch/doc/doxygen'
make[3]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[3]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/libfswatch'
Making all in fswatch
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
Making all in src
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
make[2]: Nothing to be done for 'all'.
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/src'
Making all in doc
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[2]: Nothing to be done for 'all'.
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch/doc'
make[2]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[2]: Nothing to be done for 'all-am'.
make[2]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/fswatch'
Making all in po
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha/po'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha/po'
make[1]: Entering directory '/home/g/Downloads/fswatch-1.19.0-alpha'
make[1]: Nothing to be done for 'all-am'.
make[1]: Leaving directory '/home/g/Downloads/fswatch-1.19.0-alpha'

[emcrisostomo]

Hey! Thanks for trying this out.

Would your approach potentially create duplicate file creation events in the case the watch was fast enough, and then you scan to emit a synthetic creation event, or are you somehow handling that too?
File creation events could be duplicated and fswatch is not currently handling that case: since those events could be delivered after the synthetic ones are created, it would require to keep that list in memory for some time.

On the building: everything you've done is correct! To write on /usr/local you generally need elevated privileges, so using sudo was correct. Now, the reason why the library is not found is just because the dynamic linker information, which is cached, has not been updated. To update it, you need to run ldconfig (that's run on boot), but you can run it manually. I replicated your problem in an Ubuntu instance:

fswatch: error while loading shared libraries: libfswatch.so.13: cannot open shared object file: No such file or directory

Then:

vscode ➜ /workspaces/fswatch/build (master) $ sudo ldconfig
vscode ➜ /workspaces/fswatch/build (master) $ fswatch
Invalid number of arguments.