Modification time preservation issue using SMB in certain configurations with ReadyNASOS 6

Hi!

I ran across a quite weird behaviour where modification time stamps of the local file system were not preserved after copying the file to a SMB share on my Netgear ReadyNAS 214 from a Linux client. After copying, the file received the current time as modification time instead. That behaviour seems to depend on certain versions of the client SMB version, the server SMB version and the negotiated SMB protocol version.

Why is that an issue? Because mirroring directories with rsync with the strategy to overwrite older files does not work properly anymore.

In a nutshell you would expect a file to look identical in terms of stat -c <the_file> on client and server after copying with either cp -p or rsync -t.  On my system using Linux Mint Mate 21.2 that was not the case against a RN214 running ReadyNASOS 6.10.8 with Linux 4.4.218.alpine.1 kernel and Samba version 4.8.0 (running protocol SMB3_11). Updating the client(!) kernel to Linux 6.5.0-14-generic then fixed it. Tendentially, more recent SMB versions seem to expose cleaner behaviour.

Read all the gory details at bugs.launchpad.net/ubuntu.

To find out, if your system is affected, I suggest creating and running this shell script (sorry for the messy formatting, the forum software does not seem to let me properly paste a raw text file as "code sample"):

#!/bin/bash
# Shell script to verify SMB timestamp integrity.
# Changelog:
# 1.0: Initial Linux release.
version="1.0"

# Directories.
source_dir=~/Temp
target_dir=/media/rn214/user/Temp

# Sleep duration [s].
sleep_duration=10

# Color codes.
RED='\033[0;31m'
GREEN='\033[0;32m'
NC='\033[0m' # No Color

# Show usage information.
usage() {
echo "Usage: ${0##*/} [source_dir] [target_dir]"
echo "Creates temporary file at [source_dir], copies it over to [target_dir] with 'cp -p' and 'rsync -t',"
echo "then compares timestamps of source and target file."
echo "Defaults:"
echo " source_dir=$source_dir, target_dir=$target_dir."
exit 1
}

# Show client system details.
sysdetails() {
echo "Client system details:"
hostnamectl
echo "Kernel:"
uname -r
echo "Samba version:"
samba -V
echo "Please run 'hostnamectl', 'uname -r' and 'samba -V' (or 'sudo smbstatus') on your SMB server to determine versions."
}

# Strip off path from filename.
strip_path() {
filename="$1"
filename_without_path="${filename##*/}" # Strip off path.
echo "$filename_without_path"
}

echo "This is ${0##*/} V. $version, a tool to verify SMB timestamp integrity."

if [ "$1" == "-h" ] || [ "$1" == "--help" ]; then
usage
fi
if [ "$1" != "" ]; then
source_dir="$1"
fi
if [ "$2" != "" ]; then
target_dir="$2"
fi
if ! [ -d "$source_dir" ]; then
echo "Error: Source directory '$source_dir' does not exist."
exit 2
fi
if ! [ -d "$target_dir" ]; then
echo "Error: Target directory '$target_dir' does not exist."
exit 3
fi

temp_file="$(strip_path "$(mktemp -u)")"
source_path="$source_dir/$temp_file"
target_path="$target_dir/$temp_file"

echo "Creating '$temp_file' file at: '$source_dir'..."
rm -f "$source_path" &>/dev/null
rm -f "$target_path" &>/dev/null
head -c 1k </dev/urandom >"$source_path"
touch -t "202001011234.56" "$source_path"

echo
echo "cp -p $source_path $target_path..."
cp -p "$source_path" "$target_path"
echo "cp complete; sleeping $sleep_duration second(s) before stat..."
# We sleep, as smbd actually does work after the cp -p returns.
# An immediate stat may return the current time for the modified timestamp
# even though it will be corrected shortly.
sleep $sleep_duration

source_time=$(stat -c "%y" "$source_path")
target_time=$(stat -c "%y" "$target_path")
echo "Source modtime: $source_time"
echo "Target modtime: $target_time"
if [ "$source_time" = "$target_time" ]; then
echo -e "${GREEN}cp PASS: Modtime preserved.${NC}";
else
echo -e "${RED}cp FAIL: Modtime not preserved!${NC}";
sysdetails
fi
rm -f "$target_path" &>/dev/null

echo
echo "rsync -t $source_path $target_path..."
rsync -t "$source_path" "$target_path"
echo "rsync complete; sleeping $sleep_duration second(s) before stat..."
sleep $sleep_duration

target_time=$(stat -c "%y" "$target_path")
echo "Source modtime: $source_time"
echo "Target modtime: $target_time"
if [ "$source_time" = "$target_time" ]; then
echo -e "${GREEN}rsync PASS: Modtime preserved.${NC}";
else
echo -e "${RED}rsync FAIL: Modtime not preserved!${NC}";
sysdetails
fi

echo
echo "Cleaning up..."
rm -f "$source_path" &>/dev/null
rm -f "$target_path" &>/dev/null

echo "Done. Thank you for using ${0##*/}."

Adapt source_dir and target_dir accordingly. If you get mismatches, unfortunately there is no guaranteed recipe for success, as all kernels and SMB version react differently. Perhaps rather use NFS shares if you do not have to operate in a mixed environment.

I also cannot tell if Windows clients are affected as well and which version of Microsoft Windows would that be.