Linux: Difference between revisions

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Linux is a free Unix-type operating system originally created by [http://en.wikipedia.org/wiki/Linus_Torvalds Linus Torvalds] with the assistance of developers around the world. Developed under the [http://www.linux.org/info/gnu.html GNU General Public License] , the source code for Linux is freely available to everyone.
Linux is a free Unix-type operating system originally created by [http://en.wikipedia.org/wiki/Linus_Torvalds Linus Torvalds] with the assistance of developers around the world. Developed under the [http://www.linux.org/info/gnu.html GNU General Public License] , the source code for Linux is freely available to everyone.


== Links ==
== Links ==
*[[linux kernel]]
*[[Distributions]]


*[[Linux_kernel|linux kernel]]
*[[Distributions|Distributions]]
*https://kb.novaordis.com/index.php/Events_OS_Metrics
*Linux on ircnet: #linux2
 


== Rescue CDs ==
== Rescue CDs ==
*[https://www.scientificlinux.org/downloads/ Scientific Linux]


*[[SystemRescueCd]]
*[https://www.scientificlinux.org/downloads/ Scientific Linux]
*[http://www.knoppix.net/ Knoppix]
 
*[[SystemRescueCd|SystemRescueCd]]  
*[http://www.knoppix.net/ Knoppix]  
 
 
 


== Administration ==


==Checking resources==
*[https://chrisdown.name/2018/01/02/in-defence-of-swap.html About swap]
*inxi
*[http://www.suse.de/~agruen/acl/linux-acls/online/ POSIX ACLS]
*http://www.slashroot.in/linux-system-io-monitoring
*[[LVM|LVM]]
===show what is doing most disk accesses===
*[[Linux_Software_Raid|Linux Software Raid]]
iotop
*[http://www-128.ibm.com/developerworks/library/l-bootload.html Boot loader showdown: Getting to know LILO and GRUB]
glances


===IO statistics===
*[[Linux_Power_Management|Linux Power Management]]
iostat
vmstat
dstat
ioping
atop


===CPU usage etc===
 
top
atop
htop
vtop
fio
pidstat


==Administration==
*[https://chrisdown.name/2018/01/02/in-defence-of-swap.html About swap]
*[http://www.suse.de/~agruen/acl/linux-acls/online/ POSIX ACLS]
*[[LVM]]
*[[Linux Software Raid]]
*[http://www-128.ibm.com/developerworks/library/l-bootload.html Boot loader showdown: Getting to know LILO and GRUB]


*[[Linux Power Management]]


==FAQ==
===check if virtual of physicalmachine===
dmidecode -s system-manufacturer
virt-who


= FAQ =
==Storage==
===Umount: /mnt/sda1 is busy===
Try
umount -lf /mnt/sda1


=== Grow (GPT) last partition to max available ===


===pam_succeed_if(sudo:auth): requirement "uid >= 1000" not met===
===Grow (GPT) last partition to max available===
Where '3' is partition number
Where '3' is partition number
  parted /dev/sdf resize 3 100%
  parted /dev/sdf resize 3 100%
No longer allowed?
No longer allowed?


  gdisk
  gdisk


===timestamp to human readable===
===I deleted a file but disk is still full===
  date -d @1522142497
It was in use by process, you'll need to kill that
===List hardware===
lsof -nP | grep '(deleted)'
*lshw
etc
*dmidecode
 
*lsusb
 
*hwinfo
===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
 
 
=== pam_succeed_if(sudo:auth): requirement "uid >= 1000" not met ===
 
 
 
 
 
=== List hardware ===
 
*lshw  
*dmidecode  
*lsusb  
*hwinfo  
*lspci
*lspci
*lscpu


  dmidecode -t baseboard
  dmidecode -t baseboard


===BLKRRPART: Device or resource busy===
=== BLKRRPART: Device or resource busy ===
 
spend all day or reboot
spend all day or reboot


 


=== calling ioclt to re-read partition table: Device or resource busy ===


===calling ioclt to re-read partition table: Device or resource busy===


=== rescan partition table ===


===rescan partition table===
Keep an eye on


Keep an eye on
  cat /proc/partitions
  cat /proc/partitions


Partition(s) have been written, but we have been unable to inform the kernel of the change
Partition(s) have been written, but we have been unable to inform the kernel of the change
  partprobe
  partprobe
  kpartx /dev/sdg
  kpartx /dev/sdg
  partx -uv /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
  echo 1 > /sys/block/sde/device/rescan
Only one that seemed to work on (centos7.x)
Only one that seemed to work on (centos7.x)
  echo "- - -" > /sys/class/scsi_host/host2/scan
  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
  blockdev --rereadpt /dev/sdg
but may throw blockdev: ioctl error on BLKRRPART: Device or resource busy


maybe
maybe
  hdparm -z /dev/sdg
  hdparm -z /dev/sdg


===Force reboot===
=== Force reboot ===
 
I found sometimes 'reboot' and 'shutdown' don't work in virtual machines, in that case try:
I found sometimes 'reboot' and 'shutdown' don't work in virtual machines, in that case try:
  #sync
  #sync
  echo s > /proc/sysrq-trigger
  echo s > /proc/sysrq-trigger
Line 105: Line 149:
  echo b > /proc/sysrq-trigger
  echo b > /proc/sysrq-trigger


===Mignight commander/dialog strange characters===
==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:
Quick fix:
  export LANG=en_US.ISO-8859-1
  export LANG=en_US.ISO-8859-1


This probleem seems to be related to screen/su -
This probleem seems to be related to screen/su -


[[Category: System Administration]]
=== kpartx failing silently ===
[[Category: Linux]]
 
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}'
  [[Category:System Administration]] [[Category:Linux]]
 
 
 
 
 
==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 :)

Latest revision as of 08:10, 25 July 2024

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

 

Rescue CDs

 


Administration

 



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


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

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 :)

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