Re: Configuration files are not resilient to power failure

Thanks a lot.

Josef 

----- Original Message -----
| From: "Robert Story" <[email protected]>
| To: "Josef Ridky" <[email protected]>
| Cc: [email protected]
| Sent: Saturday, May 5, 2018 7:00:23 AM
| Subject: Re: Configuration files are not resilient to power failure
| 
| I've added a call to fsync in 5-7-patches and master.
| 
| On Mon, 15 Jan 2018 04:18:57 -0500 (EST) Josef wrote:
| JR> net-snmp's configuration files are not resilient to power
| JR> failure.
| JR>
| JR> following a power failure event users created with
| JR> net-snmp-create-v3-user are missing from /etc/snmp/snmpd.conf
| JR> and that /var/lib/net-snmp/snmpd.conf is empty.
| JR>
| JR> Steps to Reproduce:
| JR>
| JR>   [root@rhel73 ~]# cat /etc/fstab
| JR>   UUID=8c3e7419-f4b9-425a-b535-b6849a6e68bf / xfs defaults 0 0
| JR>   [root@rhel73 ~]# grep
| JR> testuser /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
| JR> [root@rhel73 ~]# ls
| JR> -l /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
| JR> -rw-------. 1 root root 18891 Dec  4 22:32 /etc/snmp/snmpd.conf
| JR> -rw-------. 1 root root  1073 Dec  5
| JR> 00:04 /var/lib/net-snmp/snmpd.conf
| JR>
| JR>   [root@rhel73 ~]# systemctl stop snmpd
| JR>   [root@rhel73 ~]# /usr/bin/net-snmp-create-v3-user -A testpass
| JR> testuser
| JR>
| JR>   [root@rhel73 ~]# ls
| JR> -l /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
| JR> -rw-------. 1 root root 18877 Dec  5 00:09 /etc/snmp/snmpd.conf
| JR> -rw-------. 1 root root  1112 Dec  5
| JR> 00:09 /var/lib/net-snmp/snmpd.con [root@rhel73 ~]# grep
| JR> testuser /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
| /etc/snmp/snmpd.conf:rwuser
| JR> testuser /var/lib/net-snmp/snmpd.conf:createUser testuser MD5
| JR> "testpass" DES
| JR>
| JR>   [root@rhel73 ~]# systemctl start snmpd
| JR>
| JR> Force power off and reconnect.
| JR>
| JR>   [root@rhel73 ~]#  grep
| JR> testuser /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
| JR> [root@rhel73 ~]#  ls
| JR> -l /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
| JR> -rw-------. 1 root root 18861 Dec  5 00:09 /etc/snmp/snmpd.conf
| JR> -rw-------. 1 root root     0 Dec  5
| JR> 00:09 /var/lib/net-snmp/snmpd.conf
| JR>
| JR> Actual results:
| JR>
| JR>   The added user has been lost from the configuration.
| JR>   The entire /var/lib/net-snmp/snmpd.conf has been lost.
| JR>
| JR> Expected results:
| JR>
| JR>   /etc/snmp/snmpd.conf contains the newly added user.
| JR>   /var/lib/net-snmp/snmpd.conf  is not destroyed.
| JR>
| JR> Additional info:
| JR>
| JR>   This was observed for XFS root filesystems, it may be that
| JR> the default Ext's data=ordered mode behaves differently.
| JR> Running this under strace snmpd is doing a rename/rewrite of
| JR> the file. But it never calls fsync, so for the XFS case the
| JR> dirty buffers are still in memory when the box is powered off,
| JR> only the rename and create have hit the disk.
| 

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