Bug 4262

The implementation might be different, but I think the key problem here is under which condition should we enable postinst logging.

'debug-tweaks', in my point of view, seems to be a good sign.
After all, we usually enable postinst logging for debugging purpose.

//Chen Qi

As far as logging on the host goes, we typically log almost everything, so it should always be logged there. For the target, you may be right, debug-tweaks is probably the preferred way to do this; however the postinstall scripts themselves should not be changed dependent on whether or not debug-tweaks is in IMAGE_FEATURES. Either it should be handled through the package manager, or the scripts should check for the presence of a file/config option within the image which would be set at image post-processing time dependent on whether or not debug-tweaks is in IMAGE_FEATURES.

Design

Goal:
1. Enable postinst logging if 'debug-tweaks' is in IMAGE_FEATURES
2. Make rpm, opk and dpkg not dependent on IMAGE_FEATURES and POSTLOG

Implementation:
1. The run-postinst scripts will log outputs and errors if /etc/.enable_postinst_logging is present.
2. The log location is always /var/log/postinstall.log. Do not allow configuration, because this is mainly for debugging purpose and /var/log/postinstall.log is a good place. Making it configurable is not necessary.

Proof-of-concept patch
[For rpm package backend, others are similar]
diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index 2b42e12..fc5e23c 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -175,6 +175,8 @@ MACHINE_POSTPROCESS_COMMAND ?= ""
 ROOTFS_POSTPROCESS_COMMAND_prepend = "run_intercept_scriptlets; "
 # Allow dropbear/openssh to accept logins from accounts with an empty password string if debug-tweaks is enabled
 ROOTFS_POSTPROCESS_COMMAND += '${@base_contains("IMAGE_FEATURES", "debug-tweaks", "ssh_allow_empty_password; ", "",d)}'
+# Enable postinst logging if debug-tweaks is enabled
+ROOTFS_POSTPROCESS_COMMAND += '${@base_contains("IMAGE_FEATURES", "debug-tweaks", "postinst_enable_logging; ", "",d)}'
 
 # some default locales
 IMAGE_LINGUAS ?= "de-de fr-fr en-gb"
@@ -484,6 +486,11 @@ ssh_allow_empty_password () {
        fi
 }
 
+# Enable postinst logging if debug-tweaks is enabled
+postinst_enable_logging () {
+       touch ${IMAGE_ROOTFS}/etc/.enable_postinst_logging
+}
+
 # Turn any symbolic /sbin/init link into a file
 remove_init_link () {
        if [ -h ${IMAGE_ROOTFS}/sbin/init ]; then
diff --git a/meta/recipes-devtools/rpm/rpm-postinsts.bb b/meta/recipes-devtools/rpm/rpm-postinsts.bb
index 3d2d05d..ae0e37e 100644
--- a/meta/recipes-devtools/rpm/rpm-postinsts.bb
+++ b/meta/recipes-devtools/rpm/rpm-postinsts.bb
@@ -11,10 +11,6 @@ inherit allarch
 #
 POSTINSTALL_INITPOSITION ?= "98"
 
-POSTLOG ?= "/var/log/postinstall.log"
-REDIRECT_CMD = "${@base_contains('IMAGE_FEATURES', 'debug-tweaks', '>>${POSTLOG} 2>&1', '', d)}"
-REDIRECT_CMD[vardepsexclude] += "IMAGE_FEATURES POSTLOG"
-
 do_fetch() {
        :
 }
@@ -40,7 +36,12 @@ if [ "x$D" != "x" ] && [ -f $D/var/lib/rpm/Packages ]; then
 [ -d /etc/rpm-postinsts ] && for i in `ls /etc/rpm-postinsts/`; do
        i=/etc/rpm-postinsts/$i
        echo "Running postinst $i..."
-       if [ -f $i ] && $i ${REDIRECT_CMD}; then
+       if [ -x $i ]; then
+               if [ -e /etc/.enable_postinst_logging ]; then
+                       $i >/var/log/postinstall.log 2&>1
+               else
+                       $i
+               fi
                rm $i
        else
                echo "ERROR: postinst $i failed."

merged into poky/master: f7b639e527a65f9ce77aef07651ac5ec1e094e52

Verified with master/31e6eee860b5f9f4ac9ef0889bcff5648de6e3f9

Test case:

Steps:
1. Add the following lines to a .bb file. For expample, man_1.6g.bb:

pkg_postinst_${PN} () {
       #!/bin/sh -e
       if [ x"$D" = "x" ]; then
       echo "List directory to check the output log"
       ls /
       echo "List nonexist directory to check the stderr redirection log"
       ls /nonexist
       else
       exit 1
       fi
}

2. Add the following line in conf/local.conf to make sure this package is installed in the rootfs:

CORE_IMAGE_EXTRA_INSTALL += "man"

Make sure the feature "debug-tweaks" is added in conf/local.conf

3. Build a image.

4. Boot up the image and check the /var/log/postinstall.log

Expected results:
The /var/log/postinstall.log should exist in the first boot. The content of this log is like below:

Running postinst /etc/rpm-postinsts/man...
List directory to check the output log
bin
boot
dev
etc
home
lib
lost+found
media
mnt
proc
run
sbin
sys
tmp
usr
var
List nonexist directory to check the stderr redirection log
ls: /nonexist: No such file or directory