执行RPM更新时如何保留旧配置/元数据文件

问题拆解与解决方案 #

Let's break down your problem and walk through the solutions step by step:

1. How to implement the requirement

The core idea is to delay overwriting the old file Y1 until after the system reboots, which requires combining RPM's installation scripts with a system startup service. Here's the workflow:

• Backup the old Y1 before installing the new RPM.
• Install the updated Y1 to a temporary location instead of overwriting the original directly.
• Set up a one-time service that runs after the next system reboot to replace the old Y1 with the new one.
• Handle rollback scenarios in case the new RPM is uninstalled before reboot.

2. Are rpmsave/rpmnew suitable?

Short answer: No, they don't fit this specific requirement. Here's why:

• .rpmsave is only created automatically if the existing Y1 was modified by the user (differs from the original content in the old RPM). If Y1 is unmodified, RPM will overwrite it immediately—violating your need to keep the old file until reboot.
• .rpmnew applies to %config(noreplace) files. When a new RPM has an updated config file, it saves the new version as .rpmnew instead of overwriting the modified old file. But this doesn't automate the replacement after reboot—you'd have to manually swap them later, which isn't what you want.

These features are designed for handling user-modified files, not scheduling delayed overwrites regardless of file state.

3. Concrete Example

Let's assume your package is named mypkg, and the file Y1 is /etc/mypkg/config.yaml. Here's how to adjust the RPM spec file for version 2 (rpm2):

Step 1: Adjust the file installation path

In the %files section of your spec file, install the updated Y1 to a temporary path instead of the original:

%files
/etc/mypkg/config.yaml.new
/usr/lib/systemd/system/mypkg-post-update.service
# Include other files from your package here

Step 2: Backup the old Y1 in the %pre script

Add a pre-install script to save the existing Y1 if it exists:

%pre
# Create backup directory if it doesn't exist
mkdir -p /var/lib/mypkg/backups
# Backup the old config file
if [ -f /etc/mypkg/config.yaml ]; then
    cp -a /etc/mypkg/config.yaml /var/lib/mypkg/backups/config.yaml.old
fi

Step 3: Create a systemd one-shot service for post-reboot replacement

Create a service file mypkg-post-update.service with the following content:

[Unit]
Description=Apply mypkg config update after system reboot
After=multi-user.target  # Run after the system reaches multi-user mode

[Service]
Type=oneshot
# Replace the old config with the new one
ExecStart=/usr/bin/mv -f /etc/mypkg/config.yaml.new /etc/mypkg/config.yaml
# Clean up the backup after successful replacement
ExecStartPost=/usr/bin/rm -rf /var/lib/mypkg/backups
# Mark the service as completed after running
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Step 4: Enable the service in the %post script

After installing the RPM, reload systemd and enable the service to run on next reboot:

%post
systemctl daemon-reload
systemctl enable --now mypkg-post-update.service

Step 5: Handle rollback in %postun script

If the user uninstalls rpm2 before rebooting, restore the old Y1 and clean up:

%postun
# $1 equals 0 when performing a full uninstall
if [ $1 -eq 0 ]; then
    # Disable and stop the service
    systemctl disable --now mypkg-post-update.service
    # Restore the old config file if backup exists
    if [ -f /var/lib/mypkg/backups/config.yaml.old ]; then
        mv -f /var/lib/mypkg/backups/config.yaml.old /etc/mypkg/config.yaml
        rm -rf /var/lib/mypkg/backups
    fi
    # Remove the temporary new config file
    rm -f /etc/mypkg/config.yaml.new
fi

Usage

Install the RPM as usual:

rpm -Uvh mypkg-2.0.rpm

After installation:

• The old /etc/mypkg/config.yaml remains intact.
• The new config is at /etc/mypkg/config.yaml.new.
• The systemd service is enabled to run on the next reboot.

Once the system reboots, the service will automatically replace the old config with the new one, completing the update.

内容的提问来源于stack exchange，提问作者xyz