Red Hat Bugzilla – Bug 620401
sed overwrites symlinks
Last modified: 2013-02-05 18:55:45 EST
Description of problem: sed overwrites symlinks and creates ordinary file instead. This is a Regression of bz#189016. Version-Release number of selected component (if applicable): sed-4.2.1-5.el6 How reproducible: 100% Steps to Reproduce: 1. touch src 2. ln -s src lnk 3. sed -i 's.o.n.g' lnk Actual results: lnk is overwritten Expected results: lnk not overwritten Additional info:
This change was done in Fedora 11 and is by design. RHEL 3 included this change without even looking at the manual or contacting upstream. In doing so it deviated unnecessarily from what is documented in its own "info sed", from upstream, from basically all other Linux distros, and also from "perl -i" behavior. The implementation was also bad, since there are bugs in symlink following in RHEL5 -- bug #490473 -- while realpath(3) could have been used much more simply... RHEL6 sed provides --follow-symlinks which achieves this behavior. I suggest documenting it in the release notes.
From the sed manual of RHEL6 `-i' clobbers read-only files In short, `sed -i' will let you delete the contents of a read-only file, and in general the `-i' option (*note Invocation: Invoking sed.) lets you clobber protected files. This is not a bug, but rather a consequence of how the Unix filesystem works. The permissions on a file say what can happen to the data in that file, while the permissions on a directory say what can happen to the list of files in that directory. `sed -i' will not ever open for writing a file that is already on disk. Rather, it will work on a temporary file that is finally renamed to the original name: if you rename or delete files, you're actually modifying the contents of the directory, so the operation depends on the permissions of the directory, not of the file. For this same reason, `sed' does not let you use `-i' on a writeable file in a read-only directory, and will break hard or symbolic links when `-i' is used on such a file. Everything except "and will break hard or symbolic links when `-i' is used on such a file" is present also in RHEL5 (however it could be inferred from the description, which says it is renaming a temporary file to the original name).
See also http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=339793 (comments #31 to #51 -- that's just five comments actually).
Scott, Migration Guide text in comment 3
Scott, this is a Migration Guide blocker for 6.0
Note added to Migration Guide. Changes will appear on next publish.