Linux – How to easily repair a single unreadable block on a Linux disk

hard drivelinuxlvmsmartsmartctl

My Linux system has started throwing SMART errors in the syslog. I tracked it down and believe the problem is a single block on the disk. How do I go about easily getting the disk to reallocate that one block? I'd like to know what file got destroyed in the process. (I'm aware that if one block fails on a disk others are likely to follow; I have a good ongoing backup and just want to try to keep this disk working.)

Searching the web leads to the Bad block HOWTO, which describes a manual process on an unmounted disk. It seems complicated and error-prone. Is there a tool to automate this process in Linux? My only other option is the manufacturer's diagnostic tool, but I presume that'll clobber the bad block without any reporting on what got destroyed. Worst case, it might be filesystem metadata.

The disk in question is the primary system partition. Using ext3fs and LVM. Here's the error log from syslog and the relevant bit from smartctl.

smartd[5226]: Device: /dev/hda, 1 Currently unreadable (pending) sectors

Error 1 occurred at disk power-on lifetime: 17449 hours (727 days + 1 hours)
... Error: UNC at LBA = 0x00d39eee = 13868782

There's a full smartctl dump on pastebin.

Best Answer

You could try hdparm --write-sector <LBA> /dev/ice.

I don't know any other way of doing this - you need to manually convert the LBA into filesystem blocks (as you've already found)

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Linux Hard Disk Load – How to Monitor Hard Disk Load on Linux

You can get a pretty good measure of this using the iostat tool.

% iostat -dx /dev/sda 5

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.78    11.03    1.19    2.82    72.98   111.07    45.80     0.13   32.78   1.60   0.64

The disk utilisation is listed in the last column. This is defined as

Percentage of CPU time during which I/O requests were issued to the device (band-width utilization for the device). Device saturation occurs when this value is close to 100%.

Linux – How to run a server on port 80 as a normal user on Linux

Short answer: you can't. Ports below 1024 can be opened only by root. As per comment - well, you can, using CAP_NET_BIND_SERVICE, but that approach, applied to java bin will make any java program to be run with this setting, which is undesirable, if not a security risk.

The long answer: you can redirect connections on port 80 to some other port you can open as normal user.

Run as root:

# iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080

As loopback devices (like localhost) do not use the prerouting rules, if you need to use localhost, etc., add this rule as well (thanks @Francesco):

# iptables -t nat -I OUTPUT -p tcp -d 127.0.0.1 --dport 80 -j REDIRECT --to-ports 8080

NOTE: The above solution is not well suited for multi-user systems, as any user can open port 8080 (or any other high port you decide to use), thus intercepting the traffic. (Credits to CesarB).

EDIT: as per comment question - to delete the above rule:

# iptables -t nat --line-numbers -n -L

This will output something like:

Chain PREROUTING (policy ACCEPT)
num  target     prot opt source               destination         
1    REDIRECT   tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:8080 redir ports 8088
2    REDIRECT   tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:80 redir ports 8080

The rule you are interested in is nr. 2, so to delete it:

# iptables -t nat -D PREROUTING 2

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