On Linux operating systems, the shred to overwrite a file to hide its contents, and optionally delete it.
The shred program was created by the GNU project. On non-Linux operating systems, it has the command name gshred.
shred is a program that will overwrite your files in a way that makes them very difficult to recover by a third party.
Normally, when you delete a file, that portion of the disk is marked as being ready for another file to be written to it, but the data is still there. If a third party were to gain physical access to your disk, they could, using advanced techniques, access the data that you thought you had deleted.
The analogy is that of a paper shredder. If you crumple up a piece of paper and throw it in the trash can, a third party could come along, root through your trash, and find your discarded documents. If you really want to destroy the document, it's best to use a paper shredder. Or burn it, I suppose, but that's not always practical in a typical office.
The way that shred accomplishes this type of destruction digitally is to overwrite (over and over, repeatedly, as many times as you specify) the data you want to destroy, replacing it with other (usually random) data. Doing this magnetically destroys the data on the disk and makes it highly improbable that it can ever be recovered.
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shred 語法
shred [OPTIONS]FILE[...]
shred [OPTIONS]FILE[...]
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shred 選項
-f, --force
如有必要，更改權限以允許寫入。
-n, --iterations=N
覆蓋N次而不是默認值（3）。
-s, --size=N
切碎這么多字節（接受后綴，如K，M，G）。
-u, --remove
覆蓋后截斷并刪除文件。
-v, --verbose
顯示有關切碎進度的詳細信息。
-x, --exact
不要將文件大小四舍五入到下一個完整的塊；這是非常規文件（例如設備名稱）的默認設置。
-z, --zero
添加最終的零覆蓋以隱藏切碎。
-
切碎標準輸出。
--help
顯示此幫助并退出。
--version
輸出版本信息并退出。
-f, --force
Change permissions to allow writing if necessary.
-n, --iterations=N
Overwrite N times instead of the default (3).
-s, --size=N
Shred this many bytes (suffixes like K, M, G accepted).
-u, --remove
Truncate and remove file after overwriting.
-v, --verbose
Show verbose information about shredding progress.
-x, --exact
Do not round file sizes up to the next full block; this is the default for non-regular files such as device names.
-z, --zero
Add a final overwrite with zeros to hide shredding.
After destroying the FILE data, shred will also delete the FILE(s) if --remove (-u) is specified. The default is not to remove the files because it is common to operate on entire device files like /dev/hda, and those files usually should not be removed. When operating on regular files, most people use the --remove option.
CAUTION: Take note that shred relies on an important assumption: that the file system overwrites data "in-place." This assumption is the traditional way to do things, but many modern file systems do not do things exactly this way. The following are examples of file systems on which shred is not effective, or is not guaranteed to be effective in all file system modes:
log-structured or journaled file systems, such as those supplied with AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
file systems that write redundant data and carry on even if some writes fail, such as RAID-based file systems
file systems that make snapshots, such as Network Appliance's NFS server
file systems that cache in temporary locations, such as NFS version 3 clients
compressed file systems
In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which journals file data in addition to file metadata. In both the data=ordered (default) and data=writeback modes, shred works as usual. Ext3 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file, as documented in the mount manual.
Also, file system backups and remote mirrors may contain copies of the file that cannot be removed, and that will allow a shredded file to be recovered later.
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shred 示例
shred file1.txt file2.jpg file3.doc
使用默認的分解方法覆蓋file1.txt、file2.jpg和file3.doc的數據。
shred -u file1.txt file2.jpg file3.doc
同上，但也要刪除這三個文件，釋放磁盤上的空間供以后使用。
shred /dev/hda6
覆蓋分區/dev/hda6上的所有數據。
shred file1.txt file2.jpg file3.doc
Overwrite the data of file1.txt, file2.jpg, and file3.doc using the default shredding methods.
shred -u file1.txt file2.jpg file3.doc
Same as above, but also delete those three files, freeing up that space on the disk for later use.
shred (覆蓋文件以隱藏其內容，并有選擇地刪除它)
在Linux操作系統上，一種分解操作，它覆蓋一個文件以隱藏其內容，并有選擇地刪除它。 shred程序是由GNU項目創建的。在非Linux操作系統上，它的命令名為gshred。
On Linux operating systems, the shred to overwrite a file to hide its contents, and optionally delete it. The shred program was created by the GNU project. On non-Linux operating systems, it has the command name gshred.
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1 shred 運行系統環境
2 shred 描述
3 shred 語法
4 shred 選項
5 shred 示例
shred 運行系統環境
Unix&Linux
shred 描述
通常，當您刪除一個文件時，磁盤的那部分被標記為準備好寫入另一個文件，但數據仍然存在。如果第三方獲得對磁盤的物理訪問權，他們可以使用高級技術訪問您認為已刪除的數據。
這個比喻就是碎紙機。如果你把一張紙揉成一團扔進垃圾桶里，第三方就會出現，在你的垃圾堆里翻找，找到你丟棄的文件。如果你真的想銷毀文件，最好用碎紙機。或者把它燒掉，但在一個典型的辦公室里，這并不總是實用的。
shred以數字方式完成這種類型的銷毀的方法是覆蓋（一遍又一遍，重復，按指定的次數）要銷毀的數據，用其他（通常是隨機的）數據替換它。這樣做會破壞磁盤上的數據，使其極不可能被恢復。
Normally, when you delete a file, that portion of the disk is marked as being ready for another file to be written to it, but the data is still there. If a third party were to gain physical access to your disk, they could, using advanced techniques, access the data that you thought you had deleted.
The analogy is that of a paper shredder. If you crumple up a piece of paper and throw it in the trash can, a third party could come along, root through your trash, and find your discarded documents. If you really want to destroy the document, it's best to use a paper shredder. Or burn it, I suppose, but that's not always practical in a typical office.
The way that shred accomplishes this type of destruction digitally is to overwrite (over and over, repeatedly, as many times as you specify) the data you want to destroy, replacing it with other (usually random) data. Doing this magnetically destroys the data on the disk and makes it highly improbable that it can ever be recovered.
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shred 語法
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shred 選項
銷毀文件數據后，如果指定了--remove（-u），則shred還將刪除文件。默認情況下不刪除這些文件，因為在像/dev/hda這樣的整個設備文件上操作是很常見的，而且這些文件通常不應該被刪除。當操作常規文件時，大多數人使用--remove選項。 注意：請注意，shred依賴于一個重要的假設：文件系統“就地”覆蓋數據。這個假設是傳統的方法，但許多現代文件系統并不是這樣做的。以下是文件系統的示例，其中“碎片”在所有文件系統模式下都無效或不能保證有效： 日志結構或日志文件系統，如AIX和Solaris（以及JFS、ReiserFS、XFS、Ext3等）提供的文件系統 寫入冗余數據并在某些寫入失敗時仍繼續執行的文件系統，如基于RAID的文件系統 生成快照的文件系統，如Network Appliance的NFS服務器 在臨時位置緩存的文件系統，如nfsversion3客戶端 壓縮文件系統 對于ext3文件系統，上面的免責聲明只適用于data=journal模式，除了文件元數據外，還記錄文件數據。在data=ordered（默認）和data=writeback模式下，shred與平常一樣工作。Ext3日志記錄模式可以通過將data=something選項添加到/etc/fstab文件中特定文件系統的裝載選項中來更改，如裝載手冊中所述。 此外，文件系統備份和遠程鏡像可能包含無法刪除的文件副本，這將允許以后恢復碎片文件。
After destroying the FILE data, shred will also delete the FILE(s) if --remove (-u) is specified. The default is not to remove the files because it is common to operate on entire device files like /dev/hda, and those files usually should not be removed. When operating on regular files, most people use the --remove option. CAUTION: Take note that shred relies on an important assumption: that the file system overwrites data "in-place." This assumption is the traditional way to do things, but many modern file systems do not do things exactly this way. The following are examples of file systems on which shred is not effective, or is not guaranteed to be effective in all file system modes: log-structured or journaled file systems, such as those supplied with AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.) file systems that write redundant data and carry on even if some writes fail, such as RAID-based file systems file systems that make snapshots, such as Network Appliance's NFS server file systems that cache in temporary locations, such as NFS version 3 clients compressed file systems In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which journals file data in addition to file metadata. In both the data=ordered (default) and data=writeback modes, shred works as usual. Ext3 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file, as documented in the mount manual. Also, file system backups and remote mirrors may contain copies of the file that cannot be removed, and that will allow a shredded file to be recovered later.
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shred 示例
使用默認的分解方法覆蓋file1.txt、file2.jpg和file3.doc的數據。
同上，但也要刪除這三個文件，釋放磁盤上的空間供以后使用。
覆蓋分區/dev/hda6上的所有數據。
Overwrite the data of file1.txt, file2.jpg, and file3.doc using the default shredding methods.
Same as above, but also delete those three files, freeing up that space on the disk for later use.
Overwrite all data on the partition /dev/hda6.
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其他命令行
sysklogd | s2p | service | sag | set | setenv | setfacl | sfdisk | sha224sum | sha256sum | sha384sum | sha512sum | shutdown | sleep | stat | startx | strftime | strip | swapoff |