In relatively new 20.04.1 installation, xmllint will not read files

Asked by Syd Bauman

Is this a bug, or something I am doing wrong? Or both?

The `xmllint` command (of libxml2 fame) will not open any local files. The `xmlstarlet` command also will usually not open files, I presume because it is relying on libxml2 to open and parse them, but I do not know that.

Here is a shell console listing to demonstrate the problem.

$ #
$ # version of system and xmllint itself
$ #
$ cat /etc/os-release
| NAME="Ubuntu"
| VERSION="20.04.1 LTS (Focal Fossa)"
| ID=ubuntu
| ID_LIKE=debian
| PRETTY_NAME="Ubuntu 20.04.1 LTS"
| VERSION_ID="20.04"
$ which xmllint
| /snap/bin/xmllint
$ xmllint --version
| /snap/libxml2/69/bin/xmllint: using libxml version 20909-GITv2.9.9
| compiled with: Threads Tree Output Push Reader Patterns Writer SAXv1 FTP HTTP DTDValid HTML Legacy C14N Catalog XPath XPointer XInclude Iconv ISO8859X Unicode Regexps Automata Expr Schemas Schematron Modules Debug Zlib Lzma
$ #
$ # input document
$ #
$ cat /tmp/tiny_duck.xml
| <?xml version="1.0" encoding="UTF-8"?>
| <duck>
| <sound>quack</sound>
| </duck>
$ #
$ # try it (it fails)
$ #
$ xmllint --format /tmp/tiny_duck.xml
| I/O error : Permission denied
| I/O error : Permission denied
| warning: failed to load external entity "/tmp/tiny_duck.xml"
$ #
$ # Could it actually be a permissions problem?
$ # No, I just `cat`ted that file. But double-check,
$ # anyway.
$ #
$ ls -l /tmp/tiny_duck.xml
| -rw-rw-r-- 1 syd syd 78 Jan 6 08:27 /tmp/tiny_duck.xml
$ whoami
| syd
$ #
$ # try a different command that reads and parses XML on same file
$ #
$ which xmlwf
| /usr/bin/xmlwf
$ xmlwf -v
| xmlwf using expat_2.2.9
| sizeof(XML_Char)=1, sizeof(XML_LChar)=1, XML_DTD, XML_CONTEXT_BYTES=1024, XML_NS
$ xmlwf -s -m -d /tmp/ERASE.ME/ /tmp/tiny_duck.xml
$ cat /tmp/ERASE.ME/tiny_duck.xml
| <document>
| <starttag name="duck" uri="/tmp/tiny_duck.xml" byte="39" nbytes="6" line="2" col="0"/>
| <chars str="&#10;" uri="/tmp/tiny_duck.xml" byte="45" nbytes="1" line="2" col="6"/>
| <chars str=" " uri="/tmp/tiny_duck.xml" byte="46" nbytes="2" line="3" col="0"/>
| <starttag name="sound" uri="/tmp/tiny_duck.xml" byte="48" nbytes="7" line="3" col="2"/>
| <chars str="quack" uri="/tmp/tiny_duck.xml" byte="55" nbytes="5" line="3" col="9"/>
| <endtag name="sound" uri="/tmp/tiny_duck.xml" byte="60" nbytes="8" line="3" col="14"/>
| <chars str="&#10;" uri="/tmp/tiny_duck.xml" byte="68" nbytes="1" line="3" col="22"/>
| <endtag name="duck" uri="/tmp/tiny_duck.xml" byte="69" nbytes="7" line="4" col="0"/>
| </document>

Help *greatly* appreciated, for although I am sure I can live without `xmllint` and `xmlstarlet`, I cannot get any work done without them. I will be forced to revert to 16.04 (or some other earlier release; or some other flavor of GNU/Linux).

Thank you.

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Ubuntu libxml2 Edit question
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Solved by:
Syd Bauman
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Manfred Hampl (m-hampl) said :

You are not using the *.deb version from the Ubuntu repositories, but the snap version, hence you are wrong here.
For applications in snap format you better ask at

And yes, it is an access rights problem. Snap applications usually are not allowed accessing the /tmp directory.
Copy the file into your home directory and xmllint might be able to read it.

Revision history for this message
Syd Bauman (syd-bauman) said :

Thank you, m-hampl!

You have both solved my problem, and incorrectly identified it. It was not an outright access problem with /tmp/, as it did not matter if the input file was in /tmp/ or in ~/Documents/, I got the same result. (And, as a side question which belongs in the snapverse, I suppose, why on earth would an application not be allowed to access /tmp/? Seems nuts to me.) However, uninstalling the snap version of libxml2 and installing both libxml2 and libxml2-utils with the usual `sudo apt install` did the trick.

I suppose to be a good dooby I should go report this problem on snapcraft as you suggest. That said, I have not gotten any work done for days, I would like to just get back to it ... :-|

Thank you again.