最近在清理苹果笔记本空间时，发现一个奇怪的现象，不论删除多少文件，空间就是让不出来，度娘、谷哥都用上了，就是没有查到解决办法，于是乎我决定亲自出马，自己动手、丰衣足食。

苹果自带的磁盘管理工具是diskutil，

查看该命令时，发现有个参数应该能清理空间(此处提醒各位看官，对磁盘的一切操作关乎到数据的完整性及安全性，所以一定要慎重、慎重、再慎重)

zyjsupers-MacBook-Air:etc root# diskutil

Disk Utility Tool

Utility to manage local disks and volumes

Most commands require an administrator or root user

WARNING: Most destructive operations are not prompted

Usage:  diskutil [quiet] <verb> <options>, where <verb> is as follows:

...........

     eraseDisk            (Erase an existing disk, removing all volumes)

     eraseVolume          (Erase an existing volume)

     reformat            (Erase an existing volume with same name and type)

     eraseOptical        (Erase optical media (CD/RW, DVD/RW, etc.))

     zeroDisk            (Erase a disk, writing zeros to the media)

     randomDisk          (Erase a disk, writing random data to the media)

     secureErase          (Securely erase a disk or freespace on a volume)

上面这些参数都是磁盘清理的命令，其中secureErase这个参数的解释是安全清理一块磁盘的空间(看仔细哦，是对一块磁盘进行清理，非常危险的参数)或者一个逻辑卷的空闲空间。

执行下这个命令，可以看到参数如下：

zyjsupers-MacBook-Air:etc root# diskutil secureErase

Usage:  diskutil secureErase [freespace] level

        MountPoint|DiskIdentifier|DeviceNode

"Securely" (but see "man diskutil") erases either a whole disk

or a volume's freespace. Level should be one of the following:

        0 - Single-pass zeros.

        1 - Single-pass random numbers.

        2 - US DoD 7-pass secure erase.

        3 - Gutmann algorithm 35-pass secure erase.

        4 - US DoE 3-pass secure erase.

Ownership of the affected disk is required.

Note: Level 2, 3, or 4 secure erases can take an extremely long time.

如果加上freespace这个参数就是清理空闲空间，反之则是清理整块磁盘(危险！！！！！)，如果是清理空闲空间的话请切记添加freespace这个参数。

5个清理级别，0 level代表用数字0填充磁盘空间，速度较快，其他几个速度较慢。

看下Man手册中的相关介绍：

secureErase[freespace]leveldevice

                Erase, using a "secure" (but see the NOTE below) method, either a whole-disk (including all of its partitions

                if partitioned), or, only the free space (not in use for files) on a currently-mounted volume.  Secure erasing

                makes it harder to recover data using "file recovery" software.

                Erasing a whole-disk will leave it useless until it is partitioned again.  Erasing freespace on a volume will

                leave your files intact, indeed, from an end-user perspective, it will appear unchanged, with the exception

                that it will have attempted to make it impossible to recover deleted files.

                If you need to erase all contents of a partition but not its hosting whole-disk, use thezeroDiskor

               randomDiskverbs.  Ownership of the affected disk is required.

               Levelshould be one of the following:

                     o  0 - Single-pass zero-fill erase.

                     o  1 - Single-pass random-fill erase.

                     o  2 - US DoD 7-pass secure erase.

                     o  3 - Gutmann algorithm 35-pass secure erase.

                     o  4 - US DoE algorithm 3-pass secure erase.

                NOTE: This kind of secure erase is no longer considered safe. Modern devices have wear-leveling, block-spar-

                ing, and possibly-persistent cache hardware, which cannot be completely erased by these commands. The modern

                solution for quickly and securely erasing your data is encryption. Strongly-encrypted data can be instantly

                "erased" by destroying (or losing) the key (password), because this renders your data irretrievable in practi-

                cal terms.  Consider using APFS encryption (FileVault).

仔细阅读下man手册，整理了一条专用清理空闲空间的命令如下：

zyjsupers-MacBook-Air:etc root#  diskutil secureErase freespace 0 disk2s1

大概花费了20多分钟，清理出70GB的空闲空间，没发现有其他异常。也不知道什么原理。

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