LinuxQuestions.org - neonsignal

reverse ssh connections

Posted 05-23-2011 at 05:01 AM by neonsignal
Updated 05-23-2011 at 05:06 AM by neonsignal

Setting up a reverse ssh connection can be useful when the destination machine is inside a NAT, and a port cannot be forwarded to it (eg, a work LAN), but an ssh in the reverse direction is possible.

Because the destination machine must set up the reverse connection automatically, the autossh utility can be used to keep the ssh connection alive so that it doesn't time out. From the destination machine:

Code:

autossh -f -p client-ssh-port -R reverse-ssh-port:localhost:22 client-ip

...

neonsignal

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closing ports

Posted 05-22-2011 at 06:10 AM by neonsignal

The default debian installation only has a few daemons listening on ports. These can be also closed if desired (assuming they are not being used).

The rpcbind port (111) can be closed by removing the portmap package. Since it is used by nfs, this facility will also be removed:

Code:

apt-get autoremove portmap

The auth port (113) can be closed by commenting out the ident line in the server configuration database /etc/inetd.conf. The daemon is stopped...

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annotating PDF files

Posted 05-19-2011 at 10:55 AM by neonsignal

Filling in PDF forms can sometimes be annoying, especially when the forms are DRM controlled (and do not provide edit fields).

A useful utility is flpsed. It isn't a PDF editor as such; instead, it allows the addition of text annotations to PDF files by tacking them on to the end of the file, which means that it works on just about any PDF.

Font size and color can be selected. The annotation set can be saved separately if required, and it can also be used from the command...

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migrating a system to a new disk

Posted 05-18-2011 at 05:16 AM by neonsignal
Updated 05-18-2011 at 05:18 AM by neonsignal

This is a procedure for migrating a whole system to a new disk (such as when upgrading the primary disk in a machine). The new disk is installed alongside the old one (either in a spare ATA port, or using a USB adapter).

First partition the new disk (the examples here assume the original disk is sda and the new disk is sdb):

Code:

fdisk /dev/sdb

Assuming all of the system is to be in a single partition, make a primary partition 'n', 'p', taking most...

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upgrading ext3 to ext4 filesystem

Posted 05-18-2011 at 04:40 AM by neonsignal
Updated 05-18-2011 at 04:44 AM by neonsignal

The following commands upgrade an existing umounted ext3 filesystem to ext4 without having to reformat:

Code:

tune2fs -O extents,uninit_bg,dir_index /dev/partition
e2fsck -fDC0 /dev/partition

To upgrade the root partition, change /etc/fstab so that it will be mounted as ext4 (since ext4 can mount an ext3 file system), then reboot as single user read-only (recovery mode). Then after setting the tune2fs parameters, reboot again before running e2fsck. Then reboot...

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