Alan Wylie's Web Site

Tue, 2016-11-01

umount: /mnt/tmp: device is busy permalink

If you are trying to unmount a device, you get the error "device is busy", but lsof/fuser don't show any process holding the device open, it could be that a file on the device is associated with a loop device.

try

# losetup -a
/dev/loop/0: [0821]:25280514 (image) offset=55273881600
# losetup  -d /dev/loop0 
# umount /mnt/tmp

(updated, 2016-11-01)

dmsetup info | grep loop
dmsetup remove loop0p2
dmsetup remove loop0p3

may help too

Thu, 2016-03-03

More hints on unmounting a filesystem: permalink
(previously)

# ls -l /dev/mapper/
# dmsetup ls
# dmsetup info loop0p2
# dmsetup remove loop0p2
# losetup -a
# losetup -d loop0
# umount /mnt/tmp

Thu, 2016-02-04

Windows Security Applications (2007-12) permalink
(updated for Malwarebytes, 2016-02-04) When working with friend's PCs, here are some applications I install:

Secunia PSI Personal Software Inspector
(Added 2013-03-04) Filehippo Update Checker
(Added 2013-11-22) Colleagues also recommend Ninite
reviewed at The Register
Grisoft AVG free anti-virus
~~Lavasoft Ad-Aware~~ Not any more - see this article (2011-11-13)
Spybot-S&D
(added 2008-02-10) And one more link: Windows Sysinternals
(Added 2011-12-27) SANS ISC recommend MalwareBytes free anti-virus, OTOH: security issues,
(Added 2013-03-04) The UK government's advice

Tue, 2016-01-05

Hints on running a well-configured outgoing mail server. permalink

If you do not have a static IP address, use your ISP's mail relay (smarthost).
Make sure that there is a reverse DNS (PTR) record for your IP address. Make sure that it is not generic (e.g. wylie.me.uk, rather than client-12-34-56-78.adsl.example.org). You will need to contact your ISP to do this. (See RFC1912 section 2.1)
Make sure that doing a PTR lookup, then doing an A lookup on that domain name gives the original IP address, e.g.
```
$ host 82.68.155.89
89.155.68.82.in-addr.arpa domain name pointer wylie.me.uk.
$ host wylie.me.uk
wylie.me.uk has address 82.68.155.89
```
Get your ISP to SWIP your IP allocation, so that a whois lookup shows that it is allocated to you.
Make sure that your ISP has not listed your IP address as dynamic with any DNSBL, e.g. dul.dnsbl.sorbs.net. If necessary, get your ISP to contact the DNSBL maintainers and ask for your IP address to be delisted.
Make sure that your HELO/EHLO string is a FQDN (Fully Qualified Domain Name), e.g. "wylie.me.uk", rather than "NTSERVER", as required by RFC 2821 section 4.1.1.1

Further reading (This was originally written in 2006, some of these links may be out of date, I'm afraid):
SORBS
Spamhaus reverse DNS
Spamhaus Dynamic IP lists
Yahoo mail help
AOL Technical Standards for E-mail Delivery
AOL Reverse DNS
Messaging Anti-Abuse Working Group Sender Best Communications Practices

Sun, 2015-03-08

If you get errors trying to nfsmount your root partition during a PXE boot permalink

VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0): error -6
Please append a correct "root=" boot option; here are the available
partitions:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)

try adding "nfsvers=3" to your kernel command line

LABEL alan
  KERNEL alan/bzImage
  APPEND root=/dev/nfs nfsroot=192.168.21.1:/work/netboot/alan/nfsroot,nfsvers=3 \
         ip=dhcp nfsrootdebug vga=0x323 netconsole=@192.168.21.201/,@192.168.21.2/

Thu, 2014-11-20

Gentoo, bash, xmalloc errors permalink
In Gentoo, after turning on the bash use-flag "mem-scramble", I got emerge errors for icu and nmap:


bash: xmalloc: shell.c:1596: cannot allocate 10 bytes (0 bytes allocated)

Fri, 2013-11-08

Just to try and g**gleb*mb it: permalink
Link to a friend's NHS Anti Smoking Campaign

Mon, 2013-03-18

About me: permalink
I'm a computer hacker (in the original meaning of the word), a caver, a fell-walker, and cyclist.

mail me at alan@wylie.me.uk

Note that sending unsolicited marketing e-mail to an individual in the UK is an offence under the Privacy and Electronic Communications (EC Directive) Regulations 2003 and that the collection and processing of personal information is regulated by the Data Protection Act.

alan

Mon, 2013-02-18

Contact Me permalink

Please note that sending unsolicited marketing e-mail to an individual in the UK is an offence under Section 22 of the Privacy and Electronic Communications (EC Directive) Regulations 2003 http://www.legislation.gov.uk/uksi/2003/2426/regulation/22/made

If you are having difficulty e-mailing me, perhaps because of my anti-spam defenses, use this form (See also Hints on running a well-configured outgoing mail server )

A Panasonic Lumix DMC-TZ18 Camera

Contact me for the contents of the SD card and the return of the camera.

Sun, 2010-08-22

Lateral Cleft, Jingling Pot permalink
Photos

Thu, 2010-05-06

Confusing Apache error message permalink

If you get the following error message:

[crit] [client 10.0.0.1] (13)Permission denied: /foo/bar/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable, referer: http://example.org/

check that the permissions on the directory enable the web server user to read/access it, to fix it do something like:

find <dir> -type d | xargs chown <apache user> find <dir> -type d | xargs chmod u+rx