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

Dmesg messages

mce: [Hardware Error]: Machine check events logged

Have a look at rasdaemon and then check

ras-mc-ctl --errors

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

Assuming 3 is last partition

growpart /dev/sda 3

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. It could also be an iscsi disk that appeared, got a case with 'sd 19:0:0:0: Power-on or device reset occurred' Identify the sd number with

lsscsi

Network

check if interface exists

/sys/class/net/$IF

List disks and their sizes

lsblk -d

or

fdisk -l | grep "Disk \/dev\/sd"

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

Address already in use

lsof -i :8080

When was this linux installed?

Check for /var/log/installer

Pick a device it was installed on

DEV=/dev/sda1

and then

tune2fs -l $DEV| grep -i created

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 :)

Kernel panic - not syncing: VFS: Unable to mount root fs"

Maybe the initrd.img* for the kernel is missing.