How do you create a hardlink (as opposed to a symlink or a Mac OS alias) in OS X that points to a directory? I already know the command "ln target destination" but that only works when the target is a file. I know that Mac OS, unlike other Unix environments, does allow hardlinking to folders (this is used for Time Machine, for example) but I don't know how to do it myself.
I agree that hard-linking folders/directories can cause problems if not careful, but they have a very definite advantage - Time Machine is a perfect example. Without them it simply would not be practical as the duplication of redundant versions of files would very quickly consume even the largest of disks.
Snow Leopard can create hard links to directories as long as you follow Amit Singh's six rules:
The file system must be journaled HFS+.
The parent directories of the source and destination must be different.
The source’s parent must not be the root directory.
The destination must not be in the root directory.
The destination must not be a descendent of the source.
The destination must not have any ancestor that’s a directory hard link.
So it's not correct at all that Snow Leopard has lost the ability to create hard links to
folders.
I just verified that link/unlink do work on Snow Leopard - as long as you follow the six
rules. I just tried it and it works fine on my Snow Leopard 10.6.6 system - tried it on the boot volume and on a separate USB external volume and it worked fine in both cases.
Here is the "hunlink.c" program:
#include <stdio.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
if (argc != 2)
return 1;
int ret = unlink(argv[1]);
if (ret != 0)
perror("unlink");
return ret;
}
gcc -o hunlink hunlink.c
So, be careful if you try it - remember to follow the rules and use hlink to create these hard links and use hunlink to remove the hard link afterwards. And don't forget to document
what you've done for later on or for someone else who might need to know this.
One other "gotcha" that I just learned about these "hard links" to folders. When you create them there is really a lot that happens "behind the curtain" of Mac OS X. One really important issue is that the folder you create the link to is really moved to a super-magical super-hidden folder called /.HFS+ Private Directory Data%000d/dir_xxx where xxx is the inode number of the "source_folder" - remember the format of the command is
hlink source_folder target_folder
So because of this, you have to be careful of not having any files open in the "source_folder" because if you do, they just got moved to the super-magical folder and you will likely have a problem if you try and save any changes to those files that were open in the "source_folder". This happened to me a couple of times until it dawned on me what was happening and the solution is pretty simple. I noticed that you couldn't do a "ls -la" command any longer without getting funny errors for all the folders/directories that were in the original "source_folder" but you could do a "ls" command and all looked well.
If you run "Verify disk" in the "Disk Utility" program, you will notice that it probably complains and gives a "Volume bitmap needs minor repair for orphaned blocks" which is what just happened with the creation of the super-magical folder and the movement of the "source_folder" to it.
If you do find yourself in this situation with "orphaned blocks", first save the changed files to some other temporary location not in the volume containing the "source_folder" tree, then use "Disk Utility" to unmount and remount the volume that contains the "source_folder" or just restart the computer. Then copy the files you saved to the temporary locations back to their original locations and you should be back in business. This is what worked for me, so can't guarantee this will work for you too. So it might be a good idea to try this out on a volume you have a good backup of just in case.
It seems so very weird that all this overhead occurs just for the simple task of creating a hard link to a folder. Does anyone have any idea why Mac OS X goes to all this effort for this hard link creation to folders? Does it have something to do with the fact that this is a "journaled" file system?
I discovered the info about the super-magical, super-hidden location by reading Amit Singh's explanation of his "hfsdebug" utility. If you want more details see his web site at Amit Singh's hfsdebug utility. It's a very interesting piece of software and will tell you lots of details about HFS+ file systems. It's free and I encourage you to download it and try it out. It's no longer supported but it still works on both Snow Leopard and Leopard - basically any HFS+ supported system. You can't really do any harm with it as it's a "read-only" tool - so it's great to use to look at some details of the filesystem.
One more issue about these "hard links to folders" - once you create one and the super-magical super-secret-hidden folder gets created, it's there for good. Even if you unlink the folder that caused it to be created in the first place, this magic folder stays around. Not sure why, but it definitely does. You can use "hfsdebug" to find this out if you wish to try it out. You can also use "hfsdebug" to find out how many of these "hard links to folders" exist on a drive. For these details refer to Amit's article on the "hfsdebug" utility.
He also has another newer utility that's supported but costs. It's called fileXray and costs $79 for one person on any number of computers in the same household for a personal non-business type license. It has an extensive 173-page User Guide that you can download to see what it can do before you purchase. Unfortunately there is no trial version, so read the manual and check out the web site for more details to see if it can help you out of a jam. Learn all the details about it at their web site - see fileXray web site for more info.
There are a couple of issues you should be aware of when using these hard links to folders. If the volume that they are created on is mounted to a remote client, there can be significant problems, depending on how they are mounted. If you use AFP to mount the volume to a remote client, there are big problems as any folder that currently has a hard link to it or has ever had one but later removed, will be unable to be used as all the lower level folders (but not files) will be inaccessible from either the Finder or a Terminal window. If you try to do a simple "ls -lR" command, it will fail and give you "ls: xxx: No such file or directory" error messages for all lower level folders. If you use a Finder window to traverse the directory tree of the remote volume, the folders that are in the folder that had or has a hard link to it will simply disappear without any error when you first click on the folder name.
These problems don't appear to occur (except for the error message) if you use NFS to mount the remote client (and assuming you had a NFS server on the system that has the volume as a local HFS+ filesystem). Details on how to use NFS to mount volumes are not provided here. I used a nice program from Dr. Marcel Bresink called "NFS Manager" to help with the NFS mounts on the server and client. You can get it from his web site - just search for "Bresink NFS Manager" in your favorite search engine, but he has a free trial version so you can try before you buy. It's not that big a deal if you want to learn how to do the NFS mounts, but the "NFS Manager" makes it pretty easy to set things up and to tweak all the different settings to help optimize it. He has several other neat Mac OS X utilities too that are very reasonably priced - one called "Hardware Monitor" that lets you monitor and graph all kinds of things like power usage, temperature of CPU, speed of fans and many many other variables for both the local and remote Mac systems over extended periods of time (from minutes to days). Definitely worth checking out if you are into handy utilities.
One thing I did notice is that NFS file transfers were about 20% slower than doing them via AFP, but your "mileage may vary", so no guarantees one way or the other, but I would rather have something that works even if I have to pay a 20% performance hit as compared to having nothing work at all.
Apple is aware of the problems with hard links and remote AFP filesystems, and they refer to it as an "implentation limitation" of the AFP client - I prefer to call it what it really appears to me to be - A BUG!!! I can only hope the next release of Mac OS X fixes the problem, as I really like having the ability to use hard links to folders when it makes sense.
These notes are my own personal opinion and I don't make any warranty about their correctness so use them at your own risk. Have a good backup before you play around with these "hard links to folders" just in case something unforeseen happens. But I hope you have fun if you do decide to look a bit more into this interesting aspect of Mac OS X.
You can't do it directly in BASH then. However... I found an article here that discusses how to do it indirectly: http://www.mactech.com/articles/mactech/Vol.23/23.11/ExploringLeopardwithDTrace/index.html by compiling a simple little C program:
#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
if (argc != 3) return 1;
int ret = link(argv[1], argv[2]);
if (ret != 0) perror("link");
return ret;
}
...and build in Terminal.app with:
$ gcc -o hlink hlink.c -Wall
Piffle. On 10.5, it tells you in the man page for ln:
-d, -F, --directory
allow the superuser to attempt to hard link directories (note:
will probably fail due to system restrictions, even for the
superuser)
So yes:
sudo ln -d existing_dir new_hard_link
Give it your password, and you're not done yet. You didn't document it, did you? You must document hard linked directories; even if it's a single user machine.
Deleting is a different story: if you go about it the usual way to delete directories, you'll delete the contents. So you must "unlink" the directory:
unlink new_hard_link
There. Hope you don't wreck your filesystem!
Cross-posting this great tool which neatly solves the problem, originally posted by Sam:
To install Hardlink, ensure you've installed homebrew, then run:
brew install hardlink-osx
Once installed, create a hard link with:
hln [source] [destination]
I also noticed that unlink command does not work on snow leopard, so I added an option to unlink:
hln -u destination
Code is available on Github for those who are interested: https://github.com/selkhateeb/hardlink
Yes it's supported by the kernel and the filesystem, but since it's not intended for general usage it's not exposed to the shell.
You could probably work out which APIs Time Machine uses and wrap them in a commandline tool, but it'd be better to take the hint and steer well-clear.
The OSX version of ln cannot do it, but, as mentioned in the other answer by rich, it is possible with the GNU version of ln which is available in homebrew as gln as part of the coreutils formula. man gln lists the -d option with the OSX-specific warning provided in rich's answer. In other words, it does not work in all cases. What exactly determines whether it works or not does not seem to be documented anywhere.
As a prerequisite, install coreutils:
brew install coreutils
Now you can do:
sudo gln -d /original_folder /mirror_folder
IMPORTANT: To remove the hard link you must use gunlink:
sudo gunlink /mirror_folder
❗️❗️❗️ Using rm or Finder will also delete the original folder.
FYI: The coreutils homebrew formula provides the GNU-compatible versions of generic unix tools. Use brew list coreutils to see the full list.
As of 2018 no longer possible. APFS (introduced in MacOS High Sierra 10.13) is not compatible with directory hardlinks. See https://github.com/selkhateeb/hardlink/issues/31
My case was that I found out that from a windows virtual machine, I cannot follow symlinks. (i wanted to test some HTML pages in Internet Explorer). And my directory structure had symlinks for CSS and images folders.
My workaround to solve the problem was a different approach than the other answers implied. I used rsync to create a copy of the folder. Rsync can resolve the symlinks and copy the linked files in stead.
This solved my problem without using hard links to directories. And it's actually an easy solution if you're just working on a small set of files.
rsync -av --copy-dirlinks --delete ../htmlguide ~/src/
From the article linked to, you'll get that error if you try to create the hard link in the same directory as the original. You have to create it somewhere else.
In Linux you can use bind mount to simulate hard linking directories. Not sure about OSX
sudo mount --bind /some/existing_real_contents /else/dummy_but_existing_directory
sudo umount /else/dummy_but_existing_directory
This can also be done with built-in Perl (from Terminal) without compiling anything. My specific use case is for Google Drive (which doesn't support symbolic links), so the examples below reflect the use case.
To link your "Documents" folder to Google Drive so it's synced:
perl -e 'link "/Users/me/Documents", "/Users/me/Google Drive/Documents"'
To remove the link to your "Documents" folder from Google Drive:
sudo perl -U -e 'unlink "/Users/me/Google Drive/Documents"'
You need "root" to unlink (see "unlink" perldoc).
Another solution is to use bindfs https://code.google.com/p/bindfs/ which is installable via port:
sudo port install bindfs
sudo bindfs ~/source_dir ~/target_dir
The short answer is you can't. :) (except possibly as root, when it would be more accurate to say you shouldn't.)
Unixes only allow a set number of links to directories - ".." from within all its children and "." from within itself. Anything else is potentially a recipe for a very confused directory tree. This is/was apparently a design decision by Ken Thompson.
(Having said that, apparently Apple's Time Machine does do this :) )
in case there is no sub folder, you can try
ln folder_path/*.* target_folder
it worked for me on OSX 10.9
I am working with environment value, $PATH. And I found that $PATH includes /snap/bin directory which does not exist. What does the path work? Can I remove it from $PATH or should I leave it?
Please give me your suggestion. Thank you very much?
It is a new-new Canonical thing to bundle and distribute applications.
See for example this developer link by Canonical.
Personally, I also find it somewhat odd that they went into the top-level via /snap but Oh well.
I may yet come to use it one. So far plain docker serves me well, besides of course building .deb package the old-fashioned way.
As for removing the PATH entry: it only saves you a few bytes, plus nanoseconds in lookups and may break a future deployment involving snaps. Your box, your call. I left mine.
I saw that there is a lua plugin for eclipse and there is a docpage on the awesome main page api_doc and all the .lua files in /usr/share/awesome/lib.
So I thought it must be possible to create a Library or Execution Environment so that one has tabcompletion and docview.
So I tried making my own Execution Environment:
wrote the standard .rockspec file
downloaded the documentation made an ofline version of it and put it in docs/ folder
ziped the files and folders in /usr/share/awesome/lib
ziped all up
tried it out ... and it failed.
When I try to view a documentaion for a .lua file I get "Note: This element has no attached documentation."
Questions: Am I totaly wrong in my doing (because I have the feeling I am)? Is there any way to edit the rc.lua with tabcompletion and docview?
Koneki will probably take a while to setup, but it's definitly worth it. Going for the".doclua"(by using version 1.2) would certainly make it, but I doubt that using a script to generate the information you need, would work out on the long run.
Most likely, you'll probably pass a bit of time to define what kind of object you're dealing with every time you come across one. The right to do, would be to actually take the time to see if the object/module/inner type inherit from an another object, so can actually have more completion feature as you keep using autocomplete to go from one object to another by pressing "dot"+ctrl_space.
In an ideal world, one person could probably make it right and share to other, so they can enjoy a full featured autocomplete editor.
Found solution for eclipse.
First off the idea of setting up an Execution environment was the wrong one.
So the whole thing about downloading the doc although.
For more information on that visit eclipse Wiki for LUA Development Tool.
The right thing to do is to add a source folder which contains the /usr/share/awesome/lib directory.
The bad news is that my comment from above was totally right, which means one has to configure each .lib file in /usr/share/awesome/lib to meet the requirements of the Documentation Language described here.
Than editing the rc.lua (which one can add to the project in eclipse) works with tabcompletion and doc view.
Since the Documentation Language used in the lib files is similar to the one used by "LUA Development Tool" one has not to change many things. Maybe there are even scripts for that.
I've defined a CMakeLists.txt file for my project which works correctly.
I use the CMake GUI for generating a Visual Studio Project, and I ask to build the binaries (CMAke cache and other stuff) in the folder Build which is in the same folder where CMakeLists.txt is.
I was able to specify where the executable and the libraries have to be created.
Is there a way to specify also where the Visual Studio Solution file has to be created? I would like to have it in the root directory, but at the same time I don't want to have also all the other files that CMake creates in the Build directory.
CMake creates the Project I defined in CMakeLists.txt but also two other projects: ALL_BUILD and ZERO_CHECK. What's their utility?
I was able to avoid the creation of ZERO_CHECK by using the command set_property(GLOBAL PROPERTY USE_FOLDERS On).
Is there a way for avoiding also the creation of ALL_BUILD?
It seems you only switched to CMake very recently, as exactly those questions also popped into my head when I first started using CMake. Let's address them in the order you posted them:
I use the CMake GUI for generating a Visual Studio Project, and I ask
to build the binaries (CMAke cache and other stuff) in the folder
Build which is in the same folder where CMakeLists.txt is.
Don't. Always do an out-of-source build with CMake. I know, it feels weird when you do it the first time, but trust me: Once you get used to it, you'll never want to go back.
Besides the fact that using source control becomes so much more convenient when code and build files are properly separated, this also allows to build separate distinct build configurations from the same source tree at the same time.
Is there a way to specify also where the Visual Studio Solution file has to be created?
You really shouldn't care.
I see why you do feel that you need full control over how the solution and project files get created, but you really don't. Simply specify the target for the solution as the origin of your out-of-source build and forget about all the other files that are generated. You don't need to worry, and you don't want to worry - this is exactly the kind of stuff that CMake is supposed to take care of for you.
Ask yourself: What would you gain if you could handpick the location of every project file? Nothing, because chances are, you will never touch them anyways. CMake is your sole master now...
CMake creates the Project I defined in CMakeLists.txt but also two
other projects: ALL_BUILD and ZERO_CHECK. What's their utility? I was
able to avoid the creation of ZERO_CHECK by using the command
set_property(GLOBAL PROPERTY USE_FOLDERS On). Is there a way for
avoiding also the creation of ALL_BUILD?
Again, you really shouldn't care. CMake defines a couple of dummy projects which are very useful for certain internal voodoo that you don't want to worry about. They look weird at first, but you'll get used to their sight faster than you think. Just don't try to throw them out, as it won't work properly.
If their sight really annoys you that much, consider moving them to a folder inside the solution so that you don't have to look at them all the time.
Bottom line: CMake feels different than a handcrafted VS solution in a couple of ways. This takes some getting used to, but is ultimately a much less painful experience than one might fear.
You don't always have a choice about what your environment requires. Visual Studio's GitHub integration requires that the solution file exists in source control and is at the root of the source tree. It's a documented limitation.
The best I was able to come up with is adding this bit to CMakeList.txt:
# The solution file isn't generated until after this script finishes,
# which means that:
# - it might not exist (if this is the first run)
# - you need to run cmake twice to ensure any new solution was copied
set(sln_binpath ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.sln)
if(EXISTS ${sln_binpath})
# Load solution file from bin-dir and change the relative references to
# project files so that the in memory copy is as if it had been built in
# the source dir.
file(RELATIVE_PATH prefix
${CMAKE_CURRENT_SOURCE_DIR}
${CMAKE_CURRENT_BINARY_DIR})
file(READ ${sln_binpath} sln_content)
string(REGEX REPLACE
"\"([^\"]+).vcxproj\""
"\"${prefix}/\\1.vcxproj\""
sln_content
"${sln_content}")
# Compare the updated contents with the existing source path sln, if it
# exists and is the same we don't want to disturb VS by touching it.
set(sln_srcpath ${CMAKE_CURRENT_SOURCE_DIR}/${PROJECT_NAME}.sln)
set(old_content "")
if(EXISTS ${sln_srcpath})
file(READ ${sln_srcpath} old_content)
endif()
if(NOT old_content STREQUAL sln_content)
file(WRITE ${sln_srcpath} ${sln_content})
endif()
endif()
What would be helpful is if cmake had a way to run post generation scripts, but I couldn't find one.
Other ideas that didn't work out:
wrap cmake inside a script that does the same thing, but:
telling users to run a seperate script isn't simpler than saying to run cmake twice. Especially since needing to run cmake twice isn't a foreign concept.
put it in a pre-build step, but
building is common and changing the build is rare
changing the solution from builds inside the IDE makes it do... things
use add_subdirectory because that's suppose to finish first
it appeared to make the vcxproj's immediately, but not the sln until later, but I didn't try as hard because this adds a bunch of additional clutter I didn't want - so maybe this can be made to work
I am using F# in Visual Studio 2012 and this may seem like a dumb question but I cannot figure out how to specify include directories, specifically for binaries. I see how to do it for F# interactive using the #I directive and it works there, but the #I option is not available in the non-interactive form. The compiler error message says to use the -I compiler option. I have looked under Project Properties, where the only subsections visible are Application, Build, Build Events, Debug, and Reference Paths none of which provides any obivous way to specify an include directory path. The help system isnt much help as it seems to reference sections that are unavailable.
Well i still have the problem with VS12 but at least i have a workaround, by calling the compiler from the command line. You have to use the -r option to specify the location of the dll:
fsc -r:<complete path to dll> <fname>
However when i try the corresponding step in VS (by trying to set one of the Reference Paths) it says there are no items found in the DLL folder. So perhaps someone familiar with CS can help out