[augeas-devel] Why does Augeas fail to create new files?

Tue Dec 22 15:19:03 UTC 2015

On Tue, Dec 22, 2015 at 4:08 PM, Mol, Xavier (SCC) <xavier.mol at kit.edu>
wrote:

> Hi all,
>
> I have boiled this problem down as much as possible, ie. down to a module
> that manages a file with a single word in it (I've learned some more
> notable things about that, which are listed in PS):
>
> module Word = let lns = [ seq "words" . store Rx.word . Util.eol]
>
>
> When using this module to create new files, then we get an error:
>
> [root ~]# ls /tmp/word
> ls: cannot access /tmp/word: No such file or directory
> [root ~]# augtool -t "Word.lns incl /tmp/word"
> augtool> set /files/tmp/word/1 spam
> augtool> save
> error: Failed to execute command
> saving failed (run 'errors' for details)
> augtool> errors
> Error in /tmp/word:1.0 (parse_skel_failed)
>   Input string does not match at all
>   Lens: /usr/share/augeas/lenses/word.aug:4.12-.54:
>

Yes, that is correct. Augeas needs to be able to parse the existing content
before modifying it.

>
>
> When there already is a valid file, the module works fine:
>
> [root ~]# echo spam >/tmp/word
> [root ~]# augtool -t "Word.lns incl /tmp/word"
> augtool> print /files/tmp/word
> /files/tmp/word
> /files/tmp/word/1 = "spam"
> augtool> set /files/tmp/word/1 eggs
> augtool> save
> Saved 1 file(s)
> [root ~]# cat /tmp/word
> eggs
>
>
> Honestly, to me this looks like a bug. Even making this sole lens
> optional, to make an empty file acceptable, doesn't make the module
> functional (albeit with different error message).
>
> module Word = let lns = [ seq "words" . store Rx.word . Util.eol ]?
>
> [root ~]# augtool -t "Word.lns incl /tmp/word"
> augtool> print /files/tmp/word
> augtool> set /files/tmp/word/1 spam
> augtool> save
> error: Failed to execute command
> saving failed (run 'errors' for details)
> augtool> errors
> Error in /tmp/word:1.0 (parse_skel_failed)
>   parse can not process entire input
>   Lens: /usr/share/augeas/lenses/word.aug:4.12-.55:
>

Your file isn't empty, it contains a single newline, so your lens should be:

module Word = let lns = [ seq "words" . store Rx.word . Util.eol ] |
Util.empty

> PS)
> * There must be a label for this node (either seq, key or label), or the
> Augeas tree doesn't keep the value and it cannot be altered, too.
>

You can technically have label-less nodes, but I wouldn't recommend it
indeed.

Raphaël

* The lens must match eol, even though the file might not have one - in
> that situation, end-of-file is matched instead. 'let lns = [ seq "words" .
> store Rx.word ]' always results in parsing errors ("Get did not match
> entire input"), even if files are created like 'echo -n word >file'. Though
> if there is a proper line break before the end of file (echo word >file),
> the outcome is identical.
>
> > -----Original Message-----
> > From: Mol, Xavier (SCC)
> > Sent: Thursday, December 17, 2015 1:36 PM
> > To: Mol, Xavier (SCC); augeas-devel at redhat.com
> > Subject: RE: Why does Augeas fail to create new files?
> >
> > > ---> Creating an empty node works fine, though this should actually
> fail in my opinion (an empty file is invalid according to the lens).
> > Sorry, I have to correct this. The attached lens definition does allow
> for an empty file. However, setting lns like this:
> >
> > let lns = ( empty | comment )* . version . ( empty | comment | rule )*
> >
> > Hence, requiring at least a line with "version" in it, doesn't change
> the reported behaviour at all for me.
> >
> > Ciao,
> > Xavier.
> >
> > > -----Original Message-----
> > > From: augeas-devel-bounces at redhat.com [mailto:
> augeas-devel-bounces at redhat.com] On Behalf Of Mol, Xavier (SCC)
> > > Sent: Thursday, December 17, 2015 1:33 PM
> > > To: augeas-devel at redhat.com
> > > Subject: [augeas-devel] Why does Augeas fail to create new files?
> > >
> > > Hello Augeas experts,
> > >
> > > attached you can find the source of a custom lens for Augeas and a
> file with get and put unit tests; either file is evaluated with augparse
> > > successfully. My question is, why can I not create a new file from
> scratch with that lens, while editing existing files works just fine?
> > >
> > > In order to test the steps in between, I used augeas-1.4 and augtool:
> > >
> > > [root ~]# augtool --version
> > > augtool 1.4.0 <http://augeas.net/>
> > > Copyright (C) 2007-2011 David Lutterkort
> > > License LGPLv2+: GNU LGPL version 2.1 or later
> > >                  <http://www.gnu.org/licenses/lgpl-2.1.html>
> > > This is free software: you are free to change and redistribute it.
> > > There is NO WARRANTY, to the extent permitted by law.
> > >
> > > Written by David Lutterkort
> > >
> > > [root ~]# augtool
> > > augtool> print /augeas/load/StorageAuthzdb/*[label() != "excl"]
> > > /augeas/load/StorageAuthzdb/lens = "@StorageAuthzdb"
> > > /augeas/load/StorageAuthzdb/incl = "/etc/grid-security/storage-authzdb"
> > >
> > > ---> Currently, the node included with that lens doesn't exist.
> > > augtool> ls /files/etc/grid-security/storage-authzdb
> > > augtool> dump-xml /files/etc/grid-security/storage-authzdb
> > > <augeas match="/files/etc/grid-security/storage-authzdb"/>
> > >
> > > ---> Creating an empty node works fine, though this should actually
> fail in my opinion (an empty file is invalid according to the lens).
> > > augtool> touch /files/etc/grid-security/storage-authzdb
> > > augtool> save
> > > Saved 1 file(s)
> > > augtool> ls /files/etc/grid-security
> > > storage-authzdb = (none)
> > > augtool> dump-xml /files/etc/grid-security/storage-authzdb
> > > <augeas match="/files/etc/grid-security/storage-authzdb">
> > >   <node label="storage-authzdb"
> path="/files/etc/grid-security/storage-authzdb"/>
> > > </augeas>
> > >
> > > ---> Saving the minimal change required for a valid storage-authzdb
> file fails.
> > > augtool> set /files/etc/grid-security/storage-authzdb/version "2.1"
> > > augtool> dump-xml /files/etc/grid-security/storage-authzdb
> > > <augeas match="/files/etc/grid-security/storage-authzdb">
> > >   <node label="storage-authzdb"
> path="/files/etc/grid-security/storage-authzdb">
> > >     <node label="version">
> > >       <value>2.1</value>
> > >     </node>
> > >   </node>
> > > </augeas>
> > > augtool> save
> > > error: Failed to execute command
> > > saving failed (run 'errors' for details)
> > > augtool> errors
> > > Error in /etc/grid-security/storage-authzdb:1.0 (parse_skel_failed)
> > >   parse can not process entire input
> > >   Lens: /usr/share/augeas/lenses/storageauthzdb.aug:34.12-.75:
> > >
> > >
> > > ---> Starting over...
> > > [root ~]# rm /etc/grid-security/storage-authzdb
> > > rm: remove regular empty file `/etc/grid-security/storage-authzdb'? y
> > > [root ~]# augtool
> > >
> > > ---> Create the desired tree
> > > augtool> set /files/etc/grid-security/storage-authzdb/version "2.1"
> > >
> > > ---> Review what the lens would put as a string, which matches what I
> expect.
> > > augtool> set /in ""
> > > augtool> retrieve StorageAuthzdb.lns /in
> /files/etc/grid-security/storage-authzdb /out
> > > augtool> print /out
> > > /out = "version 2.1\n"
> > >
> > > ---> Still saving that output fails
> > > augtool> save
> > > error: Failed to execute command
> > > saving failed (run 'errors' for details)
> > > augtool> errors
> > > Error in /etc/grid-security/storage-authzdb:1.0 (parse_skel_failed)
> > >   parse can not process entire input
> > >   Lens: /usr/share/augeas/lenses/storageauthzdb.aug:34.12-.75:
> > >
> > > ---> Though when the file exists before augtool is used, everything
> seems to work.
> > > [root ~]# echo version 2.1 >/etc/grid-security/storage-authzdb
> > > [root ~]# augtool
> > > augtool> ls /files/etc/grid-security/storage-authzdb
> > > version = 2.1
> > > augtool> dump-xml /files/etc/grid-security/storage-authzdb
> > > <augeas match="/files/etc/grid-security/storage-authzdb">
> > >   <node label="storage-authzdb"
> path="/files/etc/grid-security/storage-authzdb">
> > >     <node label="version">
> > >       <value>2.1</value>
> > >     </node>
> > >   </node>
> > > </augeas>
> > > augtool> set /files/etc/grid-security/storage-authzdb/version "2.2"
> > > augtool> save
> > > Saved 1 file(s)
> > > [root ~]# cat /etc/grid-security/storage-authzdb
> > > version 2.2
> > >
> > >
> > >
> > > What am I doing wrong here?
> > >
> > > Thank you for your time,
> > > Xavier.
> > >
> > >
> > > ****
> > > Karlsruher Institute of Technology (KIT)
> > > Steinbuch Centre for Computing (SCC)
> > >
> > > B. Sc. Xavier Mol
> > > GridKa Storage Administrator and Support Manager
> > >
> > > Hermann-von-Helmholtz-Platz 1
> > > Geb. 449
> > > 76344 Eggenstein-Leopoldshafen
> > > Phone: +49 721 608 23041
> > > Email: xavier.mol at kit.edu
> > > www.kit.edu
> > > KIT - University of the State of Baden-Württemberg and National
> Large-scale Research Center of the Helmholtz Association
> > > "Since 2010, the KIT has been certified as a family-friendly
> university."
> > > ****
>
>
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-- 
Raphaël Pinson
Infrastructure Developer & Training Leader
+33 458 482 013

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