Linux

Linux is a free Unix-type operating system originally created by Linus Torvalds with the assistance of developers around the world. Developed under the GNU General Public License , the source code for Linux is freely available to everyone.

Links

• linux kernel
• Distributions
• https://kb.novaordis.com/index.php/Events_OS_Metrics
• Linux on ircnet: #linux2

 

Rescue CDs

• Scientific Linux

• SystemRescueCd
• Knoppix

 

Administration

• About swap
• POSIX ACLS
• LVM
• Linux Software Raid
• Boot loader showdown: Getting to know LILO and GRUB

• Linux Power Management

 

FAQ

Storage

Umount: /mnt/sda1 is busy

Try

umount -lf /mnt/sda1

Grow (GPT) last partition to max available

Where '3' is partition number

parted /dev/sdf resize 3 100%

No longer allowed?

gdisk

I deleted a file but disk is still full

It was in use by process, you'll need to kill that

lsof -nP | grep '(deleted)'

etc

Which disk is 0.0.3.0

lsblk -dno name,hctl

Power-on or device reset occurred

I had a case where megamaid decided to spin down "unused disks" that were in JBOD. Disable that option ot switch the controller to IT mode.

Network

check if interface exists

/sys/class/net/$IF

Hardware info

Check number of CPUs

lscpu | grep Socket

Find bios version

dmidecode -s bios-version

List hardware

• lshw
• dmidecode
• lsusb
• hwinfo
• lspci
• lscpu

dmidecode -t baseboard

BLKRRPART: Device or resource busy

spend all day or reboot

 

rescan partition table

Keep an eye on

cat /proc/partitions

Partition(s) have been written, but we have been unable to inform the kernel of the change

partprobe
kpartx /dev/sdg
partx -uv /dev/sdg (this one worked on centos 7.3!)

This one gave new disk size! Verified: CentOS 6, Ubuntu 22

echo 1 > /sys/block/sde/device/rescan

Only one that seemed to work on (centos7.x)

echo "- - -" > /sys/class/scsi_host/host2/scan

or scan all:

echo "- - -" | tee /sys/class/scsi_host/host*/scan

The winner so far:

blockdev --rereadpt /dev/sdg

but may throw blockdev: ioctl error on BLKRRPART: Device or resource busy

maybe

hdparm -z /dev/sdg

Force reboot

I found sometimes 'reboot' and 'shutdown' don't work in virtual machines, in that case try:

#sync
echo s > /proc/sysrq-trigger
#optionally umount
echo u > /proc/sysrq-trigger
#reboot
echo b > /proc/sysrq-trigger

Misc

check if you're in virtual or physical machine

dmidecode -s system-manufacturer
virt-who
lscpu
virt-what

watch which files a process opens

watch ls -l /proc/`pidof clamd`/fd

timestamp to human readable

date -d @1522142497

Mignight commander/dialog strange characters

Quick fix:

export LANG=en_US.ISO-8859-1

This probleem seems to be related to screen/su -

kpartx failing silently

No output/result when trying to create:

kpartx -lv /dev/mapper/foo

this might means the device hasn't been partitioned

No output when trying to delete:

kpartx -d /dev/mapper/foop1

means you should use

kpartx -d /dev/mapper/foo

 

 

 

Create swapfile

fallocate -l 4G /var/swapfile
mkswap /var/swapfile

Temporary:

swapon -v /var/swapfile

In fstab: /var/swapfile swap swap sw,prio=-1

swapon failed: Invalid argument

problably trying to use fallocate on rhel/centos, use dd instead

partx: error adding partition

try kpartx instead

Find maximum depth of directory

find /var/www -type d | awk -F"/" 'NF > max {max = NF} END {print max}'

Booting

Cannot open access to console, the root account is locked

You probably messed up your grub config, maybe GRUB_CMDLINE_LINUX. Boot rescue CD image :)