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Creating root-level directories and symbolic links on macOS Catalina

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 这是一篇引用文章,原文来自:https://derflounder.wordpress.com/2020/01/18/creating-root-level-directories-and-symbolic-links-on-macos-catalina/,可能部分用户打不开,毕竟是wordpress.com。。。

 
我简单的COPY一下:

One of the changes which came with macOS Catalina was the introduction of a read-only root volume for the OS. For users or environments which were used to using adding directories to the root level of the boot drive, this change meant they could no longer do that.

To address this need, Apple added a new method for creating directories at the root level which leverages Apple File System’s new firmlink functionality. Firmlinks are new in macOS Catalina and are similar in function to Unix symbolic links, but instead of only allowing travel one way (from source to destination) firmlinks allow bi-directional travel.

The use of firmlinks is exclusively reserved for the OS’s own use, but Apple has also made available what are called synthetic firmlinks. These synthetic firmlinks are how the OS enables folks to create directories and symbolic links on the read-only boot volume. For more details, please see below the jump.

 

To create a synthetic firmlink, you need to do the following:

1. Create a file in the /etc directory named synthetic.conf.
2. Make sure /etc/synthetic.conf has the following permissions:

  • root: read, write
  • wheel: read
  • everyone: read

3. In /etc/synthetic.conf, define the name(s) of the empty directory or symbolic link you want to have appear at the root level.

4. After all desired entries have been made, save the /etc/synthetic.conf file.

5. Restart the Mac to apply the changes.

For example, /etc/synthetic.conf may look like this:

XML/HTML代码
  1. # create an empty directory named "foo" at / which may be mounted over  
  2. foo  
  3.   
  4. # create a symbolic link named "bar" at / which points to  
  5. # "System/Volumes/Data/bar", a writeable location at the root of the data volume  
  6. bar     System/Volumes/Data/bar  
  7.   
  8. # create a symbolic link named "baz" at / which points to "Users/me/baz"  
  9. baz     Users/me/baz  

 

Note: In those cases where you’re creating a symbolic link and are including a path, the start point for the directory path is not /. Instead, it is the next directory level down.

To show how this works, I’ve created a directory containing installer packages located at /Users/Shared/installers.

Screen Shot 2020 01 17 at 10 46 06 PM

To create a symbolic link at the root level named installers which points to /Users/Shared/installers, I would do the following:

1. Create the /etc/synthetic.conf file if it didn’t already exist.
2. Add the following entry to the /etc/synthetic.conf file:

1
installers  Users/Shared/installers

Screen Shot 2020 01 17 at 10 32 45 PM

3. Reboot the Mac.

Note: Whomever designed this came down on the “tabs” side of the “tabs vs. spaces” debate. When creating the separation between installers and Users/Shared/installers in the /etc/synthetic.conf file, you need to use tabs. If you use spaces instead, the synthetic firmlink won’t be created.

After the reboot, you should see a symbolic link named installers at the root level of the boot volume. When you navigate to it, you should see the contents of /Users/Shared/installers.

Screen Shot 2020 01 17 at 10 33 30 PM

To remove the symbolic link, remove the relevant entry from /etc/synthetic.conf and then restart. After the reboot, the installers symbolic link should be missing from the root level of the boot volume.

Screen Shot 2020 01 17 at 10 46 15 PM

For more information, please see the synthetic.conf man page. This is available by entering the following command in Terminal on macOS Catalina:

man synthetic.conf,可以看到内容大致这样:

XML/HTML代码
  1. SYNTHETIC.CONF(5)           BSD File Formats Manual          SYNTHETIC.CONF(5)  
  2.   
  3. NAME  
  4.      synthetic.conf  
  5.   
  6. SYNOPSIS  
  7.      synthetic.conf -- synthetic symbolic link and directory manifest  
  8.   
  9. DESCRIPTION  
  10.      synthetic.conf describes virtual symbolic links and empty directories to  
  11.      be created at the root mount point. Because the root mount point is read-  
  12.      only as of macOS 10.15, physical files may not be created at this loca-  
  13.      tion. All writeable paths must reside on the data volume, which is  
  14.      mounted at /System/Volumes/Data.  
  15.   
  16.      synthetic.conf provides a mechanism for some limited, user-controlled  
  17.      file-creation at /.  The synthetic entities described in this file are  
  18.      synthesized by the kernel during early system boot. They are not physi-  
  19.      cally present on the disk, but when the system is booted, they behave as  
  20.      if they were within certain parameters.  
  21.   
  22.      synthetic.conf is intended to be used for creating mount points at /  
  23.      (e.g. for use as NFS mount points in enterprise deployments) and symbolic  
  24.      links (e.g. for creating a package manager root without modifying the  
  25.      system volume).  synthetic.conf is read by apfs.util(8) during early sys-  
  26.      tem boot.  
  27.   
  28. FORMAT  
  29.      synthetic.conf specifies a single synthetic entity per line. Each line  
  30.      may have one or two columns, separated by a tab character. If a line has  
  31.      a single column, it denotes a virtual empty directory to be created at /.  
  32.      If a line has two columns, it denotes a symbolic link at / whose link  
  33.      target is given in the second column.  
  34.   
  35.      In either case, the first column denotes the name of the entity to be  
  36.      created at /.  
  37.   
  38.      A line beginning with the # character indicates a comment that is not  
  39.      parsed.  
  40.   
  41. SYNTHETIC ENTITIES  
  42.      Synthetic entities may not be deleted at runtime. In order to delete a  
  43.      synthetic entity, it must be removed from synthetic.conf, and the host  
  44.      must be rebooted.  
  45.   
  46.      New files and directories may not be created within a synthetic empty  
  47.      directory.  
  48.   
  49. EXAMPLES  
  50.            # create an empty directory named "foo" at / which may be mounted over  
  51.            foo  
  52.   
  53.            # create a symbolic link named "bar" at / which points to  
  54.            # "System/Volumes/Data/bar", a writeable location at the root of the data volume  
  55.            bar     System/Volumes/Data/bar  
  56.   
  57.            # create a symbolic link named "baz" at / which points to "Users/me/baz"  
  58.            baz     Users/me/baz  
  59.   
  60. FILES  
  61.      /etc/synthetic.conf  
  62.   
  63. SEE ALSO  
  64.      apfs.util(8) shutdown(8) reboot(2)  
  65.   
  66. Darwin/macOS                      2 July 2019                     Darwin/macOS  

 

 

参考 一下上面的内容,可以简单的试用一下。其实还行吧。(如果图片看不到。。就忍忍吧。)
---------
说白了就是几个事
1、在/etc目录下建一个 synthetic.conf 文件
2、设定的权限是:root 读写 wheel 读 everyone 读 ,权限值为:644
3、每行一条记录,目录名和目标引用的目录 
     比如你要在根目录下映射 一个 server,对应的是 /Users/gouki/Desktop,那就直接: server /Users/gouki/Desktop 就完事了
4、重要:改完得重启。。。。
--EOF
说白了,现在不支持根目录下的ln了。只能通过这个办法。如果有特别需要就试试吧。。。
     
 
 ----
::划重点::
1、权限是644
2、两个目录之间的间隔用tab,不是空格。原例子里用的是nano编辑 ,我用vim编辑的时候,tab居然无法输入(崩溃 )
3、对应的目录前好象不需要 / 
4、多测试几次吧。我重启了三次才搞定
 



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