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### 3.9 Controlling Warning Messages

Sometimes, while performing the requested task, GNU `tar` notices some conditions that are not exactly errors, but which the user should be aware of. When this happens, `tar` issues a warning message describing the condition. Warning messages are output to the standard error and they do not affect the exit code of `tar` command.

GNU `tar` allows the user to suppress some or all of its warning messages:

`--warning=keyword`

  Control display of the warning messages identified by keyword. If keyword starts with the prefix ‘`no-`’, such messages are suppressed. Otherwise, they are enabled.

  Multiple `--warning` messages accumulate.

  The tables below list allowed values for keyword along with the warning messages they control.

#### Keywords controlling `tar` operation

all

  Enable all warning messages. This is the default.

none

  Disable all warning messages.

filename-with-nuls

  ‘`%s: file name read contains nul character`’

alone-zero-block

  ‘`A lone zero block at %s`’

#### Keywords applicable for `tar --create`

cachedir

  ‘`%s: contains a cache directory tag %s; %s`’

file-shrank

  ‘`%s: File shrank by %s bytes; padding with zeros`’

xdev

  ‘`%s: file is on a different filesystem; not dumped`’

file-ignored

  ‘`%s: Unknown file type; file ignored`’
  ‘`%s: socket ignored`’
  ‘`%s: door ignored`’

file-unchanged

  ‘`%s: file is unchanged; not dumped`’

ignore-archive

  ‘`%s: file is the archive; not dumped`’

file-removed

  ‘`%s: File removed before we read it`’

file-changed

  ‘`%s: file changed as we read it`’

failed-read

  Suppresses warnings about unreadable files or directories. This keyword applies only if used together with the `--ignore-failed-read` option. See Ignore Failed Read.

#### Keywords applicable for `tar --extract`

existing-file

  ‘`%s: skipping existing file`’

timestamp

  ‘`%s: implausibly old time stamp %s`’
  ‘`%s: time stamp %s is %s s in the future`’

contiguous-cast

  ‘`Extracting contiguous files as regular files`’

symlink-cast

  ‘`Attempting extraction of symbolic links as hard links`’

unknown-cast

  ‘`%s: Unknown file type '%c', extracted as normal file`’

ignore-newer

  ‘`Current %s is newer or same age`’

unknown-keyword

  ‘`Ignoring unknown extended header keyword '%s'`’

decompress-program

  Controls verbose description of failures occurring when trying to run alternative decompressor programs (see alternative decompression programs). This warning is disabled by default (unless `--verbose` is used). A common example of what you can get when using this warning is:

      $ tar --warning=decompress-program -x -f archive.Z
      tar (child): cannot run compress: No such file or directory
      tar (child): trying gzip

  This means that `tar` first tried to decompress `archive.Z` using `compress`, and, when that failed, switched to `gzip`.

record-size

  ‘`Record size = %lu blocks`’

#### Keywords controlling incremental extraction:

rename-directory

  ‘`%s: Directory has been renamed from %s`’
  ‘`%s: Directory has been renamed`’

new-directory

  ‘`%s: Directory is new`’

xdev

  ‘`%s: directory is on a different device: not purging`’

bad-dumpdir

  ‘`Malformed dumpdir: 'X' never used`’

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