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
Administration
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
pam_succeed_if(sudo:auth): requirement "uid >= 1000" not met
List hardware
- lshw
- dmidecode
- lsusb
- hwinfo
- lspci
- lscpu
dmidecode -t baseboard
BLKRRPART: Device or resource busy
spend all day or reboot
calling ioclt to re-read partition table: Device or resource busy
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.
