commandlinefu.com is the place to record those command-line gems that you return to again and again.
Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.
If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/
You can sign-in using OpenID credentials, or register a traditional username and password.
First-time OpenID users will be automatically assigned a username which can be changed after signing in.
Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.
Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):
Subscribe to the feed for:
In my example, the mount point is /media/mpdr1 and the FS is /dev/sdd1
/mountpoint-path = /media/mpdr1
Why this command ?
Well, in fact, with some external devices I used to face some issues : during data transfer from the device to the internal drive, some errors occurred and the device was unmounted and remounted again in a different folder.
In such situations, the command mountpoint gave a positive result even if the FS wasn't properly mounted, that's why I added the df part.
And if the device is not properly mounted, the command tries to unmount, to create the folder (if it exists already it will also work) and finally mount the FS on the given mount point.
Assumes XP/2000/2003. For Server 2008+ try offset=105,906,176 You can find this number in the System Information utility under Partition Starting Offset. UEFI based boxes you want partition 2 since the first is just the boot files (and FAT). This works with (storage side) snapshots which is handy for single file restores on NFS mounted VMware systems
This is just a proof of concept: A FILE WHICH CAN AUTOMOUNT ITSELF through a SIMPLY ENCODED script. It takes advantage of the OFFSET option of mount, and uses it as a password (see that 9191? just change it to something similar, around 9k). It works fine, mounts, gets modified, updated, and can be moved by just copying it.
USAGE: SEE SAMPLE OUTPUT
The file is composed of three parts:
a) The legible script (about 242 bytes)
b) A random text fill to reach the OFFSET size (equals PASSWORD minus 242)
c) The actual filesystem
Logically, (a)+(b) = PASSWORD, that means OFFSET, and mount uses that option.
PLEASE NOTE: THIS IS NOT AN ENCRYPTED FILESYSTEM. To improve it, it can be mounted with a better encryption script and used with encfs or cryptfs. The idea was just to test the concept... with one line :)
It applies the original idea of http://www.commandlinefu.com/commands/view/7382/command-for-john-cons for encrypting the file.
The embedded bash script can be grown, of course, and the offset recalculation goes fine. I have my own version with bash --init-file to startup a bashrc with a well-defined environment, aliases, variables.
`mount -o remount` doesn't pick up new NFS options (eg. timeo, soft, retrans, etc) so you need to do a full mount/remount cycle. This one-liner makes it quick and easy :) Update your fstab with the new options, then run it.
Replace IP address with yours IP.
This is a handy command to put into ~/.bash_logout to automatically un-mount windows shares whenever the user logs out. If you use this on as a non-root account then you'll need to append sudo before umount and the user will need to have the appropriate sudoer rights to run the /bin/umount command.
Mounts a disk-image of a hdd with partitions
Just the commands for the lvreduce I keep forgetting.
Clone a root partition. The reason for double-mounting the root device is to avoid any filesystem overlay issues. This is particularly important for /dev.
Also, note the importance of the trailing slashes on the paths when using rsync (search the man page for "slash" for more details). rsync and bash add several subtle nuances to path handling; using trailing slashes will effectively mean "clone this directory", even when run multiple times. For example: run once to get an initial copy, and then run again in single user mode just before rebooting into the new disk.
Using file globs (which miss dot-files) or leaving off the trailing slash with rsync (which will create /mnt/target/root) are traps that are easy to fall into.
Assuming we have a disk image, created by dd if=/dev/sda of=image.dd we can check the image's partition layout with fdisk -ul image.dd, then substitute "x" with starting sector of the partition we want to mount. This example assumes that the disk uses 512Byte sectors
after that, you can launch bash script in your usb drive in FAT32.
Necessary for fsck for example.
The remount functionality follows the standard way how the mount command works with options from fstab. It means the mount command doesn't read fstab (or mtab) only when a device and dir are fully specified. After this call all old mount options are replaced and arbitrary stuff from fstab is ignored, except the loop= option which is internally generated and maintained by the mount command.
It does not change device or mount point.
Once you've made the snapshot you can resume any stopped services and then back up the file system (using the snapshot) without having to worry about changed files.
When finished, the snapshot can be removed :
mdconfig -d -u 1
rm /var/.snap/snap_var_`date "+%Y-%m-%d"`
if you use disk-based swap then it can defeat the purpose of this function.
Based on the execute with timeout command in this site.
A more complex script:
# This script will check the avaliability of a list of NFS mount point,
# forcing a remount of those that do not respond in 5 seconds.
# It basically does this:
# NFSPATH=/mountpoint TIMEOUT=5; perl -e "alarm $TIMEOUT; exec @ARGV" "test -d $NFSPATH" || (umount -fl $NFSPATH; mount $NFSPATH)
for i in $@; do
echo "Checking $i..."
if ! perl -e "alarm $TIMEOUT; exec @ARGV" "test -d $i" > /dev/null 2>&1; then
echo "$SCRIPT_NAME: $i is failing with retcode $?."1>&2
echo "$SCRIPT_NAME: Submmiting umount -fl $i" 1>&2
umount -fl $i;
echo "$SCRIPT_NAME: Submmiting mount $i" 1>&2