[pca] A question about how Safe operates.

[Martin Paul]

Am 20.03.2014 16:46, schrieb McGraw, Robert P:
> Can someone explain how safe works when patching with —no-safe.

At first - keep in mind that PCA does not install patches itself, it 
uses the OS command "patchadd" for that. So PCA is not involved into 
modifying any OS files. What --safe does is documented like this:

"Sometimes a patch re-delivers and silently overwrites files which have 
been modified locally. PCA tries to overcome this issue with its safe 
patch installation mode. Before installing a patch, PCA checks all files 
listed in the patch README for local modifications. If any modified file 
is in danger of being overwritten, a warning is shown and the patch is 
skipped."

PCA collects a list of files delivered in a patch and runs "pkgchk" 
against that list. Like this, comparing the actual file size/mode/etc 
against /var/sadm/install/contents it finds out if a file has local 
modifications. If so, PCA in safe mode will skip the patch.

Often a patch includes special install scripts for files included in the 
patch, which take care that files aren't simply overwritten by patchadd. 
Sometimes the intregrate changes into existing files, leaving local 
modifications alone. Sometimes they install the new file from the patch 
with an extension ".new" and leave it to the admin to integrate the changes.

PCA has a white list of patches/files, where it knows that the relevant 
patch includes special handling, to reduce the number of false warnings.

I use PCA like that:

Install all patches with --safe. I then look at all patches which were 
skipped due to safe mode, and find out why. Then install the patches 
without --safe, and react as necessary: re-integrate local changes which 
got overwritten, integrate local changes and changes in *.new files into 
the file in question, etc.

So --safe will just tell you "ohoh, watch out, there *might* be some 
manual intervention required after installing this patch, but I can't 
tell exactly what it is".

Hope that helps,
Martin.