@@ -, +, @@ 
 there are any which will be written to and display a useful error message.
 Fixes bug 378869.
---
 pym/portage/dbapi/vartree.py       | 31 ++++++++++++++++++++++++
 pym/portage/util/checkwriteable.py | 49 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 pym/portage/util/checkwriteable.py
--- a/pym/portage/dbapi/vartree.py	
+++ a/pym/portage/dbapi/vartree.py	
@@ -28,6 +28,7 @@ portage.proxy.lazyimport.lazyimport(globals(),
 	'portage.util:apply_secpass_permissions,ConfigProtect,ensure_dirs,' + \
 		'writemsg,writemsg_level,write_atomic,atomic_ofstream,writedict,' + \
 		'grabdict,normalize_path,new_protect_filename',
+	'portage.util.checkwriteable:check_dirs_writeable',
 	'portage.util.digraph:digraph',
 	'portage.util.env_update:env_update',
 	'portage.util.listdir:dircache,listdir',
@@ -3508,6 +3509,8 @@ class dblink(object):
 		
 		This function does the following:
 		
+		calls check_dirs_writeable to verify that no files will be
+		written to read-only filesystems
 		calls self._preserve_libs if FEATURES=preserve-libs
 		calls self._collision_protect if FEATURES=collision-protect
 		calls doebuild(mydo=pkg_preinst)
@@ -3685,6 +3688,7 @@ class dblink(object):
 			eagain_error = False
 
 			myfilelist = []
+			mydirlist = []
 			mylinklist = []
 			paths_with_newlines = []
 			def onerror(e):
@@ -3717,6 +3721,9 @@ class dblink(object):
 					unicode_errors.append(new_parent[ed_len:])
 					break
 
+				relative_path = parent[srcroot_len:]
+				mydirlist.append("/" + relative_path)
+
 				for fname in files:
 					try:
 						fname = _unicode_decode(fname,
@@ -3829,6 +3836,30 @@ class dblink(object):
 			for other in others_in_slot])
 		prepare_build_dirs(settings=self.settings, cleanup=cleanup)
 
+		# Check for read-only filesystems
+		rofilesystems = check_dirs_writeable(mydirlist)
+
+		if rofilesystems:
+			msg = _("One or more files installed to this package are "
+				"set to be installed to read-only filesystems. "
+				"Please mount the filesystems below read-write "
+				"and retry.")
+			msg = textwrap.wrap(msg, 70)
+			msg.append("")
+			for f in rofilesystems:
+				msg.append("\t%s" % os.path.join(destroot,
+					f.lstrip(os.path.sep)))
+			msg.append("")
+			self._elog("eerror", "preinst", msg)
+
+			msg = _("Package '%s' NOT merged due to read-only file systems.") % \
+				self.settings.mycpv
+			msg += _(" If necessary, refer to your elog "
+				"messages for the whole content of the above message.")
+			msg = textwrap.wrap(msg, 70)
+			eerror(msg)
+			return 1
+
 		# check for package collisions
 		blockers = self._blockers
 		if blockers is None:
--- a/pym/portage/util/checkwriteable.py	
+++ a/pym/portage/util/checkwriteable.py	
@@ -0,0 +1,49 @@ 
+#-*- coding:utf-8 -*-
+# Copyright 2014 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+from __future__ import unicode_literals
+
+import re
+
+from portage.util import writemsg
+from portage.localization import _
+
+
+def check_dirs_writeable(dir_list):
+	"""
+	Use /proc/mounts to check that no directories installed by the ebuild are set to
+	be installed to	a read-only filesystem
+
+	@param dir_list: Directories installed by the ebuild
+	@type dir_list: List
+	@return:
+	1. A list of filesystems which are both set to be written to and are mounted
+	read-only, may be empty.
+	"""
+	ro_filesystems = set()
+	ro_filesystems_written = set()
+
+	try:
+		with open("/proc/mounts") as procmounts:
+			roregex = re.compile(r'(\A|,)ro(\Z|,)')
+			for line in procmounts:
+				if roregex.search(line.split(" ")[3].strip()) is not None:
+					romount = line.split(" ")[1].strip()
+					ro_filesystems.add(romount)
+
+	# If /proc/mounts can't be read, assume that there are no RO
+	# filesystems and return
+	except EnvironmentError:
+		writemsg(_("!!! /proc/mounts cannot be read"))
+		return []
+
+	if not ro_filesystems:
+		return ro_filesystems
+
+	for directory in dir_list:
+		for filesystem in ro_filesystems:
+			if re.match(filesystem, directory):
+				ro_filesystems_written.add(filesystem)
+
+	return ro_filesystems_written
--