Show swap label

blkid can be used to display the swap label:

# blkid /dev/md2
/dev/md2: TYPE="swap" LABEL="SWAP-md2"

smartctl notes

Below is a list of smartctl commands I frequently use to quickly verify disk health and status, specially when you have smartd logging errors to messages log file.

  • Print all SMART (Self-Monitoring, Analysis and Reporting Technology) information for drive /dev/sda (Primary Master).

    smartctl -a /dev/sda

  • Enable SMART on device.

    smartctl --smart=on /dev/sda

  • Get info about the device:

    smartctl -i /dev/sda

  • Show the capabilities of drive. Also provides status when tests are being carried out.

    smartctl -c /dev/sda

  • Basic health status:

    smartctl -H /dev/sda

  • Display attributes. The attributes to look out for failing disk is Reallocated_Sector_Ct, Reallocated_Event_Count, Current_Pending_Sector and Offline_Uncorrectable. Their RAW_VALUE should normally be "0".

    smartctl -A /dev/sda

  • Immediate offline test which updates attributes value. Good to run after a badblocks fsck check before checking on the attributes values.

    smartctl -t offline /dev/sda

  • Run a thorough long test if you see suspect attributes with -A option as mentioned above.

    smartctl -t long /dev/sda

  • Examine self-test log. Shows if tests failed or passed.

    smartctl -l selftest /dev/sda

  • Display most recent error log.

    smartctl -l error /dev/sda

There are more examples in man smartctl.

Non-desctructive read-write badblocks disk check

Below command can be run on unmounted partitions to do a disk check of badblocks. Use -p if you need to automatically fix issues. Single "c" will only do a badblock read test.

e2fsck -vfcc -C 0 /dev/sdb4

"-C 0" -- displays progress
"v" -- verbose output
"f" -- force check
"cc" -- read-write test

resend all mails in sendmail queue

As root you can redeliver all mail in the mail server queue via:

sendmail -v -q

mismatch_cnt is not 0

Mismatch_cnt (/sys/block/md#/md/mismatch_cnt) is the number of unsynchronized blocks in the raid.

Not much of an issue if this is reported on raid-0 or raid-1 and can be ignored. See bugzilla report: Bug 566828.

The repair is to rebuild the raid:

echo repair >/sys/block/md#/md/sync_action

This does not reset the count, but if you force a check after the rebuild is complete:

echo check >/sys/block/md#/md/sync_action

Count should return to zero. Verify with:

cat /sys/block/md#/md/mismatch_cnt

Upgrade CentOS 5.4 to 5.5 for OpenVZ containers

Edit "/vz/template/centos/5/{ARCH}/config/yum.conf", and change the base and updates repositories as below:

name=CentOS-$releasever - Base

#released updates
name=CentOS-$releasever - Updates

Do a `vzyum {VEID} clean all`.

List updates:

vzyum {VEID} list updates


vzyum {VEID} update

Confirm that all VEs' have been updated to 5.5 with:

cat /vz/root/{VEID}/etc/redhat-release

You should see "CentOS release 5.5 (Final)".

Change server timezone

To change the server timezone, just create a link to the respective zone you're on.

ln -sf /usr/share/zoneinfo/US/Eastern /etc/localtime

Check with the `date` command.

lighttpd redirect to external url if file not found

Below is a rewrite/redirect rule using url.rewrite-[repeat]-if-not-file similar to Apaches' "!-f" RewriteRule.

# Redirect to external url if image file not found
url.rewrite-if-not-file = ( "^\/images\/.*\.jpg$" => "/redirect$0" )
url.redirect = ( "^\/redirect\/(.*)$" => "http://other.domain.tld/$1" )

Deny access to .htaccess files in lighttpd

In lighttpd you can use mod_access to deny files starting with a certain expression, such as hidden dot files. (example: .htaccess or .svn)

# Deny access to hidden files
$HTTP["url"] =~ "/\." {
    url.access-deny = ("")

Find files that have not been accessed for a while

Below one liner uses the find command to list files sorted by access time beyond the provided "number of days".

find </path/to/folder> -type f -atime +<number of days> -exec ls -ultr {} \;

This becomes handy if you want to do archive and cleanup of your web folders that have grown to a huge size.

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