Linux
System
| Description | Command |
|---|---|
| Boot into CLI mode. | sudo systemctl set-default multi-user.target |
| Boot into desktop mode. | sudo systemctl set-default graphical.target |
SSH
| Description | Command |
|---|---|
| Create private/public SSH key file using 2048 bit encryption and with a comment. The command creates files under ~/.ssh folder. | ssh-keygen -b 2048 -C user@host.domain |
| Push public SSH key to a server | ssh-copy-id -p 41111 -i ~/.ssh/id_rsa.pub mhan@remote.server.com |
| Reset (SELinux) permissions related to SSH. This may be needed if all else fails to correct the issue of system not accepting public keys. | restorecon -R -v ~/.ssh |
Disk
| Description | Command |
|---|---|
| Check if GRUB is installed on a partition (e.g. /dev/sda) | sudo dd bs=512 count=1 if=/dev/sda 2>/dev/null | strings |
Search
- xargs - to be processed - Things you (probably) didn’t know about xargs
LVM
Physical volume
| Description | Command |
|---|---|
| Initialize for use as LVM physical volume. | pvcreate /dev/sdb1 |
| Scanning for block devices. | lvmdiskscan |
| Display the physical volumes. | pvdisplay |
| Show all physical devices. | pvscan |
| Prevent allocation of physical extents on the free space of one or more physical volumes. | pvchange -x n /dev/sdb1 |
| Resize. | pvresize |
| Remove LVM label. | pvremove |
Volume group
| Description | Command |
|---|---|
| Create a volume group. | vgcreate vg1 /dev/sdb1 /dev/sdc1 |
| Add a physical volume to a volume group. | vgextend vg1 /dev/sdd1 |
| Display volume group. | vgdisplay new_vg |
| Scan disks for volume groups. | vgscan |
| Remove a physical volume from a volume group. | vgreduce group_name /dev/sdc1 |
| Change the maximum number of logical volumes of volume group vg00 to 128. | vgchange -l 128 /dev/vg00 |
| Activate or deactivate a volume group. | vgchange -a n my_volume_group |
| Remove a volume group. | vgremove officevg |
| Split the physical volumes of a volume group and create a new volume group. | $ vgsplit bigvg smallvg /dev/ram15 Volume group "smallvg" successfully split from "bigvg" |
| Merge the inactive volume group my_vg into the active or inactive volume group databases giving verbose runtime information. | vgmerge -v databases my_vg |
| Change the name of a volume group. | vgrename vg02 my_volume_group |
Users
UID or GID
| Description | Command |
|---|---|
| Check UID. | id -u username |
| Check GID. | id -g username |
| Check all of the groups a user belongs to. | id -G username |
| Check UID and all of the groups a user belongs to. | id username |
File
Permissions
| Letter | Number |
|---|---|
| r | 4 |
| w | 2 |
| x | 1 |
| rw- | 6 |
| r-x | 5 |
| rwx | 7 |
Audio
ALSA (Advanced Linux Sound Architecture)
Setting default output device
Ref: StackExchange/superuser: How to make Alsa pick a preferred sound device automatically?
List all audio cards you have:
$ cat /proc/asound/cards
0 [PCH ]: HDA-Intel - HDA Intel PCH
HDA Intel PCH at 0xf7530000 irq 41
1 [NVidia ]: HDA-Intel - HDA NVidia
HDA NVidia at 0xf7080000 irq 17
2 [SoundBar ]: USB-Audio - Dell AC511 USB SoundBar
Dell Dell AC511 USB SoundBar at usb-0000:00:14.0-4, full speed
Get ALSA identifiers of those:
$ aplay -l | awk -F \: '/,/{print $2}' | awk '{print $1}' | uniq
PCH
NVidia
SoundBar
Update /etc/asound.conf:
pcm.!default {
type hw
card SoundBar
}
ctl.!default {
type hw
card SoundBar
}
I found that the numeric identifier for these cards and change on reboot. That may be related to how the hardware detection works on Linux, and the order changes time to time. So I've used the string identifier instead -- seems to stick better than a numeric value.
PulseAudio
Restart pulseaudio. Do not sudo for this.
$ pulseaudio -k && pulseaudio -D
List sinks.
$ pacmd list-sinks
1 sink(s) available.
* index: 0
name: <alsa_output.usb-Dell_Dell_AC511_USB_SoundBar-00-SoundBar.analog-stereo>
driver: <module-alsa-card.c>
flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY
state: SUSPENDED
suspend cause: IDLE
priority: 9049
volume: front-left: 26202 / 40% / -23.89 dB, front-right: 26202 / 40% / -23.89 dB
balance 0.00
base volume: 107931 / 165% / 13.00 dB
volume steps: 65537
muted: no
current latency: 0.00 ms
max request: 0 KiB
max rewind: 0 KiB
monitor source: 0
sample spec: s16le 2ch 44100Hz
channel map: front-left,front-right
Stereo
used by: 0
linked by: 0
configured latency: 0.00 ms; range is 0.50 .. 2000.00 ms
card: 1 <alsa_card.usb-Dell_Dell_AC511_USB_SoundBar-00-SoundBar>
module: 7
properties:
alsa.resolution_bits = "16"
device.api = "alsa"
device.class = "sound"
alsa.class = "generic"
alsa.subclass = "generic-mix"
alsa.name = "USB Audio"
alsa.id = "USB Audio"
alsa.subdevice = "0"
alsa.subdevice_name = "subdevice #0"
alsa.device = "0"
alsa.card = "0"
alsa.card_name = "Dell AC511 USB SoundBar"
alsa.long_card_name = "Dell Dell AC511 USB SoundBar at usb-0000:00:14.0-4, full speed"
alsa.driver_name = "snd_usb_audio"
device.bus_path = "pci-0000:00:14.0-usb-0:4:1.0"
sysfs.path = "/devices/pci0000:00/0000:00:14.0/usb3/3-4/3-4:1.0/sound/card0"
udev.id = "usb-Dell_Dell_AC511_USB_SoundBar-00-SoundBar"
device.bus = "usb"
device.vendor.id = "413c"
device.vendor.name = "Dell Computer Corp."
device.product.id = "a503"
device.product.name = "Dell AC511 USB SoundBar"
device.serial = "Dell_Dell_AC511_USB_SoundBar"
device.string = "front:0"
device.buffering.buffer_size = "352800"
device.buffering.fragment_size = "176400"
device.access_mode = "mmap+timer"
device.profile.name = "analog-stereo"
device.profile.description = "Analog Stereo"
device.description = "Dell AC511 USB SoundBar Analog Stereo"
alsa.mixer_name = "USB Mixer"
alsa.components = "USB413c:a503"
module-udev-detect.discovered = "1"
device.icon_name = "audio-card-usb"
ports:
analog-output: Analog Output (priority 9900, latency offset 0 usec, available: unknown)
properties:
active port: <analog-output>
Networking
How To Use Nmap to Scan for Open Ports on your VPS
Security
Miscellaneous
- X11 - X Window System
- i3wm - i3 window manager
- Running Steam on CentOS 7 with NVIDIA driver