Useful Things - New pages [en]

Udev

2015-09-21T14:30:32Z

Milosivanovic: Created page with "== Disable new-style interface naming == <pre> ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules </pre>"

== Disable new-style interface naming ==
<pre>
ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules
</pre>

Systemd/network

2015-09-21T14:15:36Z

Milosivanovic: Created page with "== Static IP setup == File: <code>/etc/systemd/network/wired.network</code> <pre> [Match] Name=eth0 [Network] DNS=8.8.8.8 Address=192.168.101.2/24 Address=123.123.123.123/32..."

== Static IP setup ==
File: <code>/etc/systemd/network/wired.network</code>

<pre>
[Match]
Name=eth0

[Network]
DNS=8.8.8.8
Address=192.168.101.2/24
Address=123.123.123.123/32

[Route]
Gateway=192.168.101.1
</pre>

== Additional post-up network hooks ==
File: <code>/etc/systemd/system/my-service.service</code>

<pre>
[Unit]
Description=Service description
Wants=network.target
After=network.target

[Service]
ExecStart=/usr/local/sbin/executable-to-run

[Install]
WantedBy=multi-user.target
</pre>

Sysctl

2015-08-05T15:28:38Z

Milosivanovic:

== Disable rp_filter ==
<pre>
for i in /proc/sys/net/ipv4/conf/*/rp_filter; do
echo 0 > $i
done
</pre>

=== Additional notes ===
http://unix.stackexchange.com/questions/90443/sysctl-proc-sys-net-ipv46-conf-whats-the-difference-between-all-defau 
https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt

== Ensure VLAN packets originate from the correct VLAN interface in iptables ==
<pre>
net.bridge.bridge-nf-filter-vlan-tagged = 1
net.bridge.bridge-nf-pass-vlan-input-dev = 1
</pre>

== Disable PMTU discovery ==
<code>net.ipv4.ip_no_pmtu_disc = 1</code>

The ip_no_pmtu_disc disables PMTU (Path Maximum Transfer Unit) discovery if enabled. In most cases this is good, so it is per default set to FALSE (ie, Path Maximum Transfer Unit is used). However, in some cases this is bad and may lead to broken connectivity. If you are experiencing problems like this, you should turn this option off and set your MTU to a reasonable value yourself.

Do note that MTU and PMTU are two different things. MTU tells the kernel the maximum transfer unit for our connection, but not over the whole connection to the other end. PMTU discovery tries to discover the maximum transfer unit to specific hosts, including all the intermediate hops on the way there.

The default value is that the ip_no_pmtu_disc is FALSE, as already stated. If this is set to TRUE, PMTU discovery is turned off. The ip_no_pmtu_disc takes a boolean value, in other words either an 1 or a 0, where 1 is on and 0 is off.

=== Reference ===
https://www.frozentux.net/ipsysctl-tutorial/chunkyhtml/variablereference.html

Iproute2

2015-08-03T16:38:18Z

Milosivanovic: Created page with "== Add a VLAN == <pre> ip link add link eth0 name eth0.100 type vlan id 100 </pre> == Remove a VLAN == <pre> ip link delete eth0.100 </pre>"

== Add a VLAN ==
<pre>
ip link add link eth0 name eth0.100 type vlan id 100
</pre>

== Remove a VLAN ==
<pre>
ip link delete eth0.100
</pre>

Openssl

2015-07-05T19:54:29Z

Milosivanovic: Created page with "== Generate self-signed certificate == <pre> openssl req -x509 -nodes -days 365 -newkey rsa:2048 -out out.crt -keyout out.key </pre>"

== Generate self-signed certificate ==
<pre>
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -out out.crt -keyout out.key
</pre>

Xargs

2015-06-24T16:05:58Z

Milosivanovic: Created page with "== Build argument list from previous output == <pre> command | xargs ls -l </pre> == Run command per line of previous output == <pre> command | xargs -L1 ls -l </pre> == Run..."

== Build argument list from previous output ==
<pre>
command | xargs ls -l
</pre>

== Run command per line of previous output ==
<pre>
command | xargs -L1 ls -l
</pre>

== Run piped command per line of previous output ==
<pre>
command | xargs -L1 sh -c 'command2 "$0" | command3'
</pre>

Entropy

2015-06-13T22:30:29Z

Milosivanovic: Created page with "== View available entropy == <pre> cat /proc/sys/kernel/random/entropy_avail </pre> == Increase available entropy == This is applicable to non-interactive machines such as se..."

== View available entropy ==
<pre>
cat /proc/sys/kernel/random/entropy_avail
</pre>

== Increase available entropy ==
This is applicable to non-interactive machines such as servers, and useful when generating a lot of keys.
=== Install the haveged package ===
''"The haveged project is an attempt to provide an easy-to-use, unpredictable random number generator based upon an adaptation of the HAVEGE algorithm. Haveged was created to remedy low-entropy conditions in the Linux random device that can occur under some workloads, especially on headless servers. Current development of haveged is directed towards improving overall reliablity and adaptability while minimizing the barriers to using haveged for other tasks."''
<pre>
emerge -av haveged
</pre>
and start it. It will use CPU execution timings (which are very irregular) to seed the system's RNG.

Tar

2015-06-12T20:24:26Z

Milosivanovic: Created page with "== List files in archive without extracting == <pre> tar tf <file.tar> </pre>"

== List files in archive without extracting ==
<pre>
tar tf <file.tar>
</pre>

Filefrag

2015-06-08T19:36:11Z

Milosivanovic: Created page with "== Check fragmentation information about a given file == <pre> filefrag -v /var/log/messages </pre>"

== Check fragmentation information about a given file ==
<pre>
filefrag -v /var/log/messages
</pre>

Gdisk

2015-06-02T13:21:47Z

Milosivanovic: Created page with "== Convert MBR to GPT without data loss == <pre> gdisk /dev/sdX </pre> Then type <code>w</code> as input."

== Convert MBR to GPT without data loss ==
<pre>
gdisk /dev/sdX
</pre>
Then type <code>w</code> as input.

Xorg.conf

2015-05-30T08:22:50Z

Milosivanovic: Created page with "== Xorg.conf file for QEMU/KVM VMs == <pre> # This is an Xorg configuration file for QEMU/KVM virtual machines. # It lets you run with resolutions larger than 800x600. # # Sa..."

== Xorg.conf file for QEMU/KVM VMs ==

<pre>
# This is an Xorg configuration file for QEMU/KVM virtual machines.
# It lets you run with resolutions larger than 800x600.
#
# Save it to /etc/X11/xorg.conf.
# Modify the resolution to suit your needs.
#
# If you're having problems, try booting with the flag -std-vga.

Section "Device"
Identifier "device"
Driver "vesa"
EndSection

Section "Screen"
Identifier "screen"
Device "device"
Monitor "monitor"
DefaultDepth 16
SubSection "Display"
Modes "1920x1080" "1024x768" "800x600"
EndSubSection
EndSection

Section "Monitor"
Identifier "monitor"
HorizSync 20.0 - 50.0
VertRefresh 40.0 - 80.0
Option "DPMS"
EndSection

Section "ServerLayout"
Identifier "layout"
Screen "screen"
EndSection
</pre>

Android/adb

2015-05-25T18:03:02Z

Milosivanovic:

== View Android system log file ==
<pre>
adb logcat
</pre>

Filter by tag name:
<pre>
adb logcat -s TAGNAME
</pre>

Android/fastboot

2015-05-25T18:02:22Z

Milosivanovic: Created page with "== Common fastboot commands == <pre> fastboot flash recovery recovery.img </pre> <pre> fastboot flash boot boot.img </pre> <pre> fastboot flash cache cache.img </pre> <pre> fa..."

== Common fastboot commands ==
<pre>
fastboot flash recovery recovery.img
</pre>
<pre>
fastboot flash boot boot.img
</pre>
<pre>
fastboot flash cache cache.img
</pre>
<pre>
fastboot flash userdata userdata.img
</pre>
<pre>
fastboot flash system system.img
</pre>
<pre>
fastboot reboot
</pre>

X

2015-05-25T02:07:41Z

Milosivanovic:

== User logs in successfully but is immediately redirected back to the login screen ==
Open a new TTY (CTRL+ALT+F1 through to F6) and then run:
<pre>
chown youruser:yourgroup ~/.Xauthority
</pre>

== startx fails with repeated "Invalid MIT-MAGIC-COOKIE-1" ==
<pre>
rm ~/.Xauthority*
rm ~/.ICE*
</pre>

Qemu

2015-05-21T04:15:15Z

Milosivanovic: Created page with "== Mount qcow2 image == === To start === <pre> modprobe nbd max_part=63 qemu-nbd -c /dev/nbd0 image.img mount /dev/nbd0p1 /mnt/image </pre> === To finish === <pre> umount /mn..."

== Mount qcow2 image ==
=== To start ===
<pre>
modprobe nbd max_part=63
qemu-nbd -c /dev/nbd0 image.img
mount /dev/nbd0p1 /mnt/image
</pre>

=== To finish ===
<pre>
umount /mnt/image
killall qemu-nbd
</pre>

Tune2fs

2015-05-03T03:30:37Z

Milosivanovic: Created page with "== Find filesystem creation date == <pre> tune2fs -l /dev/sdX </pre> <code>-l</code> list the contents of the filesystem superblock, including the current values of the parame..."

== Find filesystem creation date ==
<pre>
tune2fs -l /dev/sdX
</pre>
<code>-l</code> list the contents of the filesystem superblock, including the current values of the parameters that can be set via this program.

Resize2fs

2015-05-03T02:07:18Z

Milosivanovic: Created page with "== Resize ext4 partition to end of partition boundary == <pre> resize2fs /dev/sdX3 </pre> == Resize ext4 partition to specific size == <pre> resize2fs /dev/sdX3 50G </pre>"

== Resize ext4 partition to end of partition boundary ==
<pre>
resize2fs /dev/sdX3
</pre>

== Resize ext4 partition to specific size ==
<pre>
resize2fs /dev/sdX3 50G
</pre>

Miscellaneous

2015-04-07T07:48:00Z

Milosivanovic:

== How many additional threads did a process spawn? ==
<pre>
strace <process_name> 2>&1 | grep -e fork -e clone | wc -l
</pre>

== Bash currency converter ==
<pre>
cconv() {
wget -qO- "https://www.google.com/finance/converter?a=$1&from=$2&to=$3" | sed '/res/!d;s/<[^>]*>//g';
}
</pre>

<pre>
eclipse ~ # cconv 11 usd eur
11 USD = 10.3103 EUR
eclipse ~ # cconv 3 usd nzd
3 USD = 3.9888 NZD
eclipse ~ # cconv 1 usd nzd
1 USD = 1.3296 NZD
eclipse ~ # cconv 1 nzd usd
1 NZD = 0.7523 USD
</pre>

Lsof

2015-04-03T04:49:51Z

Milosivanovic: Created page with "== List open files on / in RW or W mode only == <pre> lsof / | grep -e ":digit:\+$u\|w$" </pre>"

== List open files on / in RW or W mode only ==
<pre>
lsof / | grep -e "[[:digit:]]\+$u\|w$"
</pre>

Stty

2015-03-24T13:02:32Z

Milosivanovic: Created page with "== Change terminal width == <pre>stty cols 237</pre> == Change terminal height == <pre>stty rows 63</pre>"

== Change terminal width ==
<pre>stty cols 237</pre>

== Change terminal height ==
<pre>stty rows 63</pre>

Arch/VLC

2015-03-23T04:55:35Z

Milosivanovic:

== Segmentation fault (core dumped) ==
As per https://bbs.archlinux.org/viewtopic.php?id=178486, remove the following plugins:
<pre>
libnotify_plugin.so
libkate_plugin.so
libgnomevfs_plugin.so
gui/libqt4_plugin.so
</pre>

Sgdisk

2015-03-22T12:54:01Z

Milosivanovic: /* Wipe MBR and GPT partition tables */

== Wipe MBR and GPT partition tables ==
<pre>
sgdisk -Z /dev/sdX
</pre>
<code>-Z</code> same as <code>--zap-all</code> — Zap (destroy) the GPT and MBR data structures and then exit.

Mdadm

2015-03-22T12:41:59Z

Milosivanovic:

== Remove a drive from an active array ==
<pre>
mdadm --manage /dev/md0 --fail /dev/sdX # set the drive as failed
mdadm --manage /dev/md0 --remove /dev/sdX # remove the drive from the array
</pre>

== Add a drive to an active and degraded array ==
<pre>
mdadm --manage /dev/md0 --add /dev/sdX # add the drive
</pre>

== Check array status ==
Both <code>cat /proc/mdstat</code> and <code>mdadm --detail /dev/md0</code> have detailed output about configured arrays.

== Possible issues ==
=== Array refuses to rebuild when in a degraded state and a new drive is added ===
The array might be frozen:
<pre>
root@galaxy:~# cat /sys/block/md0/md/sync_action
frozen
</pre>
So give it a nudge:
<pre>
root@galaxy:~# echo idle > /sys/block/md0/md/sync_action
root@galaxy:~# cat /sys/block/md0/md/sync_action
recover
</pre>

Benchmarks

2015-03-21T11:02:57Z

Milosivanovic:

== RAID 6 + LUKS ==

=== Environment ===
<pre>
eclipse shared # cat /proc/cpuinfo | grep name | uniq
model name : Intel(R) Xeon(R) CPU E31240 @ 3.30GHz

eclipse shared # findmnt /media/raid
TARGET SOURCE FSTYPE OPTIONS
/media/raid /dev/mapper/raid ext4 rw,relatime,stripe=384,data=ordered

eclipse shared # cat /sys/block/md0/md/stripe_cache_size
32768

eclipse shared # lshw -short -C disk
H/W path Device Class Description
=======================================================
/0/100/1/0/0.0.0 /dev/sdc disk 4TB ST4000VN000-1H41
/0/100/1/0/0.1.0 /dev/sdd disk 4TB ST4000VN000-1H41
/0/100/1/0/0.2.0 /dev/sde disk 4TB ST4000DM000-1F21
/0/100/1/0/0.3.0 /dev/sdf disk 4TB ST4000VN000-1H41
/0/100/1/0/0.4.0 /dev/sdg disk 4TB ST4000VN000-1H41
/0/100/1/0/0.5.0 /dev/sdh disk 4TB ST4000VN000-1H41
/0/1/0.0.0 /dev/sda disk 128GB Samsung SSD 840
/0/2/0.0.0 /dev/sdb disk 60GB OCZ-VERTEX3

eclipse shared # lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 119.2G 0 disk
├─sda1 8:1 0 32M 0 part
├─sda2 8:2 0 512M 0 part [SWAP]
└─sda3 8:3 0 118.7G 0 part /
sdb 8:16 0 55.9G 0 disk
├─sdb1 8:17 0 243M 0 part
├─sdb2 8:18 0 488M 0 part
└─sdb3 8:19 0 55.2G 0 part
sdc 8:32 0 3.7T 0 disk
└─md0 9:0 0 14.6T 0 raid6
└─raid 251:0 0 14.6T 0 crypt /media/raid
sdd 8:48 0 3.7T 0 disk
└─md0 9:0 0 14.6T 0 raid6
└─raid 251:0 0 14.6T 0 crypt /media/raid
sde 8:64 0 3.7T 0 disk
└─md0 9:0 0 14.6T 0 raid6
└─raid 251:0 0 14.6T 0 crypt /media/raid
sdf 8:80 0 3.7T 0 disk
└─md0 9:0 0 14.6T 0 raid6
└─raid 251:0 0 14.6T 0 crypt /media/raid
sdg 8:96 0 3.7T 0 disk
└─md0 9:0 0 14.6T 0 raid6
└─raid 251:0 0 14.6T 0 crypt /media/raid
sdh 8:112 0 3.7T 0 disk
└─md0 9:0 0 14.6T 0 raid6
└─raid 251:0 0 14.6T 0 crypt /media/raid
</pre>

=== Results ===
<pre>
eclipse shared # pwd
/media/raid/shared

eclipse shared # dd if=/dev/zero of=file bs=64M count=100 conv=fdatasync
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 19.4577 s, 345 MB/s
eclipse shared # dd if=/dev/zero of=file bs=64M count=100 conv=fdatasync
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 19.4899 s, 344 MB/s
eclipse shared # dd if=/dev/zero of=file bs=64M count=100 conv=fdatasync
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 19.7158 s, 340 MB/s
eclipse shared # dd if=/dev/zero of=file bs=64M count=100 conv=fdatasync
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 19.4337 s, 345 MB/s

eclipse shared # echo 3 > /proc/sys/vm/drop_caches
eclipse shared # dd if=file of=/dev/null bs=64M
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 11.4224 s, 588 MB/s
eclipse shared # echo 3 > /proc/sys/vm/drop_caches
eclipse shared # dd if=file of=/dev/null bs=64M
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 11.3578 s, 591 MB/s
eclipse shared # echo 3 > /proc/sys/vm/drop_caches
eclipse shared # dd if=file of=/dev/null bs=64M
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 11.1645 s, 601 MB/s
eclipse shared # echo 3 > /proc/sys/vm/drop_caches
eclipse shared # dd if=file of=/dev/null bs=64M
100+0 records in
100+0 records out
6710886400 bytes (6.7 GB) copied, 11.1897 s, 600 MB/s
</pre>

Tmux

2015-03-08T21:15:46Z

Milosivanovic: Created page with "== Setting environment variables == Press <code>CTRL+B</code> and then <code>:</code> (colon) Type the following: <pre> set-environment ENV_VAR VALUE </pre>"

== Setting environment variables ==
Press <code>CTRL+B</code> and then <code>:</code> (colon) 
Type the following:
<pre>
set-environment ENV_VAR VALUE
</pre>

Debian/dpkg

2015-02-04T06:32:27Z

Milosivanovic: Created page with "== Find out which package a file belongs to == <pre> dpkg -S `readlink -f /path/to/java` </pre>"

== Find out which package a file belongs to ==
<pre>
dpkg -S `readlink -f /path/to/java`
</pre>

Git

2015-01-16T03:20:05Z

Milosivanovic:

== Undo last commit and KEEP changes ==
<pre>
git reset --soft HEAD~1
</pre>

== Undo last commit and LOSE changes ==
<pre>
git reset --hard HEAD~1
</pre>

== List all remote branches ==
<pre>
git ls-remote --heads <remote-name>
</pre>
where <code>remote-name</code> is usually something like <code>origin</code>

== Checkout remote branch and set it up for tracking ==
Note: These instructions are specific to having cloned in this manner: <code>git clone -b <branch-name> --single-branch</code> as it only tracks the branch chosen at clone time.
<pre>
git fetch origin <branch-name>
</pre>

<pre>
git remote set-branches origin <branch-name>
</pre>

== Show contents of merge commit ==
<pre>
git show -m [SHA1]
</pre>
where <code>-m</code> means maximum verbosity, automatically implied only with non-merge commits

== View pretty git history on the console ==
<pre>
git config --global alias.lol "log --oneline --graph --decorate"
</pre>
<pre>
git lol
</pre>

== Cache CLI credentials for a certain period of time ==
<pre>
git config --global credential.helper cache
git config --global credential.helper 'cache --timeout=86400'
</pre>

Linux/Agnostic

2015-01-16T03:01:33Z

Milosivanovic: Created page with "== Finding out file creation time == Only available on ext4. Use the <code>stat</code> command - the file creation time will be denoted as the <code>Bir..."

== Finding out file creation time ==
Only available on ext4. 
Use the <code>stat</code> command - the file creation time will be denoted as the <code>Birth</code> time.

<pre>
root@milos-debian:~# stat .bashrc
File: `.bashrc'
Size: 570 Blocks: 8 IO Block: 4096 regular file
Device: fe01h/65025d Inode: 391924 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2015-01-16 01:05:05.172328004 +1300
Modify: 2010-02-01 00:52:26.000000000 +1300
Change: 2014-10-27 16:41:41.178458115 +1300
Birth: -
</pre>

If it shows up as <code>—</code> (as above), then the <code>stat</code> command does not yet support getting this information from the kernel. Thankfully, you can still get the birth time using <code>debugfs</code>:
<pre>debugfs -R 'stat <inode_number>'</pre>

''The angle quotes, < and >, are required!''

Find the file's inode number (<code>ls -li <file></code>):
<pre>
root@milos-debian:~# ls -li .bashrc
391924 -rw-r--r-- 1 root root 570 Feb 1 2010 .bashrc
</pre>

And then use it:
<pre>root@milos-debian:~# debugfs -R 'stat <391924>' /dev/vda1
Inode: 391924 Type: regular Mode: 0644 Flags: 0x80000
Generation: 2468252752 Version: 0x00000000:00000001
User: 0 Group: 0 Size: 570
File ACL: 0 Directory ACL: 0
Links: 1 Blockcount: 8
Fragment: Address: 0 Number: 0 Size: 0
ctime: 0x544dbef5:2a8c380c -- Mon Oct 27 16:41:41 2014
atime: 0x54b7acf1:29161110 -- Fri Jan 16 01:05:05 2015
mtime: 0x4b656efa:00000000 -- Mon Feb 1 00:52:26 2010
crtime: 0x544dbef5:2a8c380c -- Mon Oct 27 16:41:41 2014
Size of extra inode fields: 28
EXTENTS:
(0):1606693
</pre>

Debian//etc/network/interfaces

2015-01-07T07:59:33Z

Milosivanovic: Created page with "= DHCP setup = <pre> auto eth0 iface eth0 inet dhcp </pre> = Static IP setup = <pre> auto eth0 iface eth0 inet static address 192.168.100.2 netmask 255.255.255.248 gateway..."

= DHCP setup =
<pre>
auto eth0
iface eth0 inet dhcp
</pre>

= Static IP setup =
<pre>
auto eth0
iface eth0 inet static
address 192.168.100.2
netmask 255.255.255.248
gateway 192.168.100.1
</pre>

= Secondary IP / alias interface setup =
<pre>
auto eth0:0
iface eth0:0 inet static
address 123.123.123.123
netmask 255.255.255.255
</pre>

= Extra startup commands =
<pre>
auto eth0:0
iface eth0:0 inet static
address 123.123.123.123
netmask 255.255.255.255
up ip route change default via 192.168.100.1 dev eth0 src 123.123.123.123
</pre>

Windows/TabletPCSettings

2014-12-08T16:40:16Z

Milosivanovic: Created page with "= Opening Table PC Settings via Command Prompt = For an unknown reason, Tablet PC Settings can disappear from Control Panel. To open it using Command Prompt, run the following..."

= Opening Table PC Settings via Command Prompt =
For an unknown reason, Tablet PC Settings can disappear from Control Panel. To open it using Command Prompt, run the following command:
<pre>
%windir%\explorer.exe shell:::{80F3F1D5-FECA-45F3-BC32-752C152E456E}
</pre>

Ffmpeg

2014-11-05T05:28:09Z

Milosivanovic: Created page with "== Common arguments == <code>-ss</code> position, in seconds or hh:mm:ss[.xxx] <code>-t</code> duration from start position <code>-acodec</code> audio codec ..."

== Common arguments ==
<code>-ss</code> position, in seconds or hh:mm:ss[.xxx] 
<code>-t</code> duration from start position 
<code>-acodec</code> audio codec 
<code>-vcodec</code> video codec

== Snip media from a start time for a specified duration ==
<pre>
ffmpeg -ss 00:00:30 -t 00:00:05 -i orginalfile -vcodec copy -acodec copy newfile
</pre>

Core dump

2014-10-17T14:27:56Z

Milosivanovic: Created page with "= Enabling core dumps = The core file size is 0 by default, which results in no core being generated: <pre> sh# ulimit -a core file size (blocks, -c) 0 ... ... ... </..."

= Enabling core dumps =
The core file size is 0 by default, which results in no core being generated:
<pre>
sh# ulimit -a
core file size (blocks, -c) 0
...
...
...
</pre>

Set it to unlimited:
<pre>
sh# ulimit -c unlimited
sh# ulimit -a
core file size (blocks, -c) unlimited
...
...
...
</pre>

Ensure that the core is written to a writeable area of the system, such as <code>/tmp</code>, by modifying the value of <code>/proc/sys/kernel/core_pattern</code>:
<pre>
echo "/tmp/core.%e.%p.%h.%t" > /proc/sys/kernel/core_pattern
</pre>
<code>%e</code> program name 
<code>%p</code> pid 
<code>%h</code> hostname 
<code>%t</code> timestamp

Setfacl

2014-09-21T11:52:56Z

Milosivanovic: Created page with "= Common arguments = <code>-b</code> remove all ACL entries = What is that weird plus sign in ls -l output? = It means the file has ACLs associated with it. <pre> -rw------..."

= Common arguments =
<code>-b</code> remove all ACL entries

= What is that weird plus sign in ls -l output? =

It means the file has ACLs associated with it.

<pre>
-rw-------+ 1 root root 8569 Sep 21 01:43 file.txt
</pre>

To remove them all:

<pre>
setfacl -b file.txt
</pre>

Now it's gone.

<pre>
-rw------- 1 root root 8569 Sep 21 01:43 file.txt
</pre>

Cryptsetup

2014-08-18T13:35:30Z

Milosivanovic:

== Common arguments ==
<pre>
--verify-passphrase, -y
When interactively asking for a passphrase, ask for it twice and
complain if both inputs do not match. Advised when creating a
regular mapping for the first time, or when running luksFormat.
Ignored on input from file or stdin.
</pre>

<pre>
--verbose, -v
Print more information on command execution.
</pre>

== Create LUKS partition ==
<source lang="bash">
cryptsetup luksFormat -y -v /path/to/device
</source>

== Mount LUKS partition ==
First unlock the partition
<source lang="bash">
cryptsetup luksOpen /path/to/device device-name
</source>

Then mount it
<source lang="bash">
mount /dev/mapper/device-name /path/to/mountpoint
</source>

== Test existing passphrase ==
<source lang="bash">
cryptsetup luksOpen --test-passphrase /path/to/device
</source>

Gai.conf

2014-08-17T04:30:41Z

Milosivanovic: Created page with "= Prefer IPv4 over IPv6 = Uncomment the following line: <pre> #precedence ::ffff:0:0/96 100 </pre>"

= Prefer IPv4 over IPv6 =
Uncomment the following line:
<pre>
#precedence ::ffff:0:0/96 100
</pre>

Mount

2014-07-27T16:18:36Z

Milosivanovic:

== Mount disk image ==
<source lang="bash">
mount -oloop,offset=1048576 image.img /mnt/destination
</source>
<code>offset</code> offset (to partition) in bytes

== Mount CIFS network share ==
<source lang="bash">
mount -ousername=user,noperm //192.168.2.2/share /mnt/mountpoint
</source>
<code>noperm</code> client does not do permission checks

Virt-install

2014-07-23T09:50:13Z

Milosivanovic: Created page with "== Define and start libvirt virtual machine == <source lang="bash">virt-install --name softeng306 --ram 512 --disk /path/to/image.img,format=qcow2 --cdrom /path/to/ubuntu-14.0..."

== Define and start libvirt virtual machine ==
<source lang="bash">virt-install --name softeng306 --ram 512 --disk /path/to/image.img,format=qcow2 --cdrom /path/to/ubuntu-14.04-server-amd64.iso --graphics vnc,listen=0.0.0.0 --noautoconsole</source>

Cryptography/EncryptionComparison

2014-07-17T02:16:40Z

Milosivanovic: Created page with "= DES vs 3DES vs AES = http://stackoverflow.com/questions/5554526/comparison-of-des-triple-des-aes-blowfish-encryption-for-data"

= DES vs 3DES vs AES =
http://stackoverflow.com/questions/5554526/comparison-of-des-triple-des-aes-blowfish-encryption-for-data

Wget

2014-07-09T23:33:20Z

Milosivanovic:

== Common arguments ==
<code>-O</code> output file

== Download a file to a specific location ==
<source lang="bash">
wget http://www.google.com/ -O /dev/null
</source>

Netstat

2014-07-09T23:21:24Z

Milosivanovic: Created page with "= Common arguments = <code>-t</code> include tcp <code>-u</code> include udp <code>-l</code> show only listening sockets <code>-p</code> show PID and program..."

= Common arguments =
<code>-t</code> include tcp 
<code>-u</code> include udp 
<code>-l</code> show only listening sockets 
<code>-p</code> show PID and program name 
<code>-n</code> show numeric addresses 

== Who is listening on what port? ==
<source lang="bash">
netstat -tulpn
</source>

Curl

2014-07-08T11:12:58Z

Milosivanovic:

== Common arguments ==
<code>-I</code> request header only 
<code>-L</code> use with <code>-I</code> to follow redirects

== Check response headers ==
<source lang="bash">
curl -I http://www.google.com/
</source>

Socat

2014-07-05T02:43:47Z

Milosivanovic: Created page with "== Forward TCP packets == <source lang="bash"> socat TCP-LISTEN:[local_port],fork TCP:[remote_host]:[remote_port] </source>"

== Forward TCP packets ==
<source lang="bash">
socat TCP-LISTEN:[local_port],fork TCP:[remote_host]:[remote_port]
</source>

Sed

2014-07-04T03:09:47Z

Milosivanovic: Created page with "== Get lines between two line numbers == <source lang="bash"> sed -n '156559,157787p' Master.csv </source>"

== Get lines between two line numbers ==
<source lang="bash">
sed -n '156559,157787p' Master.csv
</source>

Scp

2014-07-04T01:40:02Z

Milosivanovic: Created page with "== Common arguments == <code>-r</code> recursive <code>-P</code> port number (default 22) == Push a file == <source lang="bash"> scp ./path/to/source user@host:/path/to..."

== Common arguments ==
<code>-r</code> recursive 
<code>-P</code> port number (default 22)

== Push a file ==
<source lang="bash">
scp ./path/to/source user@host:/path/to/destination
</source>

== Pull a file ==
<source lang="bash">
scp user@host:/path/to/source ./path/to/destination
</source>

Rsync

2014-06-30T12:01:34Z

Milosivanovic:

== Common arguments ==
<code>-a</code> same as <code>--archive</code> 
<code>-v</code> same as <code>--verbose</code> 
<code>-x</code> same as <code>--one-file-system</code> 
<code>-z</code> compress files over the network

== Push ==
<source lang="bash">
rsync -avx /path/to/source user@host:/path/to/destination
</source>

== Pull ==
<source lang="bash">
rsync -avx user@host:/path/to/source /path/to/destination
</source>

== Pull via SSH ==
<source lang="bash">
rsync -avx --progress -e 'ssh -p 1080' --exclude-from=EXCLUDE_FILESOURCE_IP:/ /
</source>
<code>-p</code> to specify alternate SSH port

SSH

2014-06-30T11:49:10Z

Milosivanovic:

== Common arguments ==
<code>-p</code> port number (default 22)

== Upload SSH public key to remote host ==
<source lang="bash">
cat /root/.ssh/id_rsa.pub | ssh root@remotehost 'cat >> /root/.ssh/authorized_keys'
</source>

== Generate public/private RSA key-pair ==
<pre>ssh-keygen -t rsa -C 'user@host.com'</pre>

== Test private key passpharse ==
<pre>ssh-keygen -y</pre>

Find

2014-06-30T11:03:12Z

Milosivanovic:

== Between dates ==

<syntaxhighlight lang="bash">
find / -newermt "27 Dec 2013" ! -newermt "1 Jan 2014"
</syntaxhighlight>
<code>-newermt</code> newer than specified modification time 
<code>!</code> invert proceeding condition

== Several matches ==
<syntaxhighlight lang="bash">
find / -xdev $ -name .DS_Store -o -name ._.DS_Store $
</syntaxhighlight>
<code>-xdev</code> stay on the current filesystem 
<code>-o</code> logical OR, use parentheses for clarity - must be escaped in bash

== Find files and do something with each ==
<syntaxhighlight lang="bash">
find . -type f -print0 | xargs -0 <command>
</syntaxhighlight>
<code>-print0</code> print the full file name on the standard output, followed by a null character (instead of the newline character that -print uses) 
<code>-0</code> input items are terminated by a null character instead of by whitespace, and the quotes and backslash are not special (every character is taken literally)

== For each directory, set the directory mtime to the oldest file's mtime ==
<pre>
oldest() { local file oldest; for file in "${1:-.}"/*; do [ "$file" -ot "$oldest" -o -z "$oldest" ] && oldest=$file; done; touch -r "$oldest" "$0";
export -f oldest
</pre>
<syntaxhighlight lang="bash">
find . -type d -exec sh -c 'oldest "$0"' {} \;
</syntaxhighlight>

== Total size of all files found ==
<syntaxhighlight lang="bash">
find . -type f -iname '*.CR2' -print0 | du --files0-from=- -hc | tail -n1
</syntaxhighlight>

MySQL

2014-06-25T02:13:10Z

Milosivanovic: Fixed headings

== Command-line ==
=== Common arguments ===
<code>-h</code> remote host 
<code>-u</code> remote user 
<code>-p</code> requires password

=== Connect to remote MySQL server ===
<source lang="bash">
mysql -h remote.host.com -u remoteuser -p
</source>

== User management ==

=== Adding a user ===
<syntaxhighlight lang="mysql">
grant all privileges on {database_name}.* to {database_user}@'%' identified by 'their_password';
</syntaxhighlight>

=== Revoking privileges ===
<syntaxhighlight lang="mysql">
revoke usage on {databse_name}.* from {database_user}@'%';
</syntaxhighlight>

=== Removing a user ===
<syntaxhighlight lang="mysql">
drop user {database_user}@'%';
</syntaxhighlight>

== Triggers ==

=== Before ===
* OLD table name does not exist here
<syntaxhighlight lang="mysql">
create trigger {trigger_name} before [update|insert|delete] on {table_name}
for each row begin
insert into {new_table} (col1, col2, col3) values (OLD.col1, OLD.col2, OLD.col3)
end
</syntaxhighlight>

=== After ===
* OLD and NEW table names can be used to access the old value and the new value respectively
<syntaxhighlight lang="mysql">
create trigger {trigger_name} after [update|insert|delete] on {table_name}
for each row begin
insert into {new_table} (col1, col2, col3) values (OLD.col1, NEW.col2, OLD.col3)
end
</syntaxhighlight>

== Importing ==

=== From CSV ===
<syntaxhighlight lang="mysql">
load data local infile 'file_name.csv' into table table_name
fields terminated by ',' enclosed by '"'
lines terminated by '\n'

(col1, col2, coln, ...)
</syntaxhighlight>

Main Page

2014-06-24T23:28:52Z

Milosivanovic:

Hi.

This is a personal wiki packed with things that are useful to me. If they are also useful to you, feel free to bookmark relevant pages.

— ''Milos''

= All pages =
{{Special:AllPages}}