FedoraCookbook - henk52/knowledgesharing GitHub Wiki

Fedora wiki

Introduction

References

Background info

Kernel

  • http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html

  • https://github.com/torvalds/linux

    • ./Documentation/sysctl/kernel.txt
    • ./include/uapi/linux/shm.h

  • shmmax Parameter: the maximum size in bytes of a single shared memory segment that a Linux process can allocate in its virtual address space.

    • Default: (ULONG_MAX - (1UL << 24))
      • include/uapi/linux/shm.h
    • It also seems to be the max total amount of shared memory a process can attach to.
      • So if SHMMAX is 3G and 3 process has allocated 2GB each, then a process can only attach to one of the pages at a time. (from RHEL3?)
    • Access to it:
      • cat /proc/sys/kernel/shmmax
      • sysctl -w kernel.shmmax=2147483648
      • echo "kernel.shmmax=2147483648" >> /etc/sysctl.conf

  • shmall: The total amount of shared memory pages that can be used system wide.

    • Please note this is in pages, not in bytes.

  • getconf PAGE_SIZE

  • ipcs -m

  • pmap -p PID

  • /proc/PID/map

    • containing the currently mapped memory regions and their access permissions.
    • The format is:
      • address perms offset dev inode pathname
    • From: Documentation/filesystems/proc.txt in the linux source tree.
    • I looks like the "inode" for shm is actually the shmid (not the key)
      • it seems that all the /SYSV are shared memory.

Cook Book

DNF

  • dnf clean all
  • Disable Delta RPMs
    • vi /etc/dnf/dnf.conf
# disable delta RPMs
deltarpm=0

Network

tcpdump

Adding static assignments in dnsmaq

See: http://docs.slackware.com/howtos:network_services:dhcp_server_via_dnsmasq

Default GW

Domain name

Find Out What Program / Service is Listening on a Specific TCP Port

Routing

IP Tables

Port forwarding to sub nets

Firewall

SFTP service

Enable user as sftp account, for remote edit

See: https://www.server-world.info/en/note?os=Fedora_25&p=ssh&f=5

  1. groupadd sftp_users
  2. usermod -G sftp_users fedora
  3. vi /etc/ssh/sshd_config
  • It seems that after the ssh_config update the users in sftp_users can only use sftp, not ssh
  • Also you can't put another users home dir in the ChrootDirectory you get a broken link.
  1. Subsystem sftp /usr/libexec/openssh/sftp-server Subsystem sftp internal-sftp
  2. add to the end
Match Group sftp_users
  X11Forwarding no
  AllowTcpForwarding no
  ChrootDirectory /home
  ForceCommand internal-sftp

devices

Detecting if there is a CDROM in the drive

See: http://superuser.com/questions/630588/how-to-detect-whether-there-is-a-cd-rom-in-the-drive

You can get information about any block device using the command blkid.

[root@arch32-vm ~]# blkid /dev/sr0
/dev/sr0: UUID="2013-05-31-23-04-19-00" LABEL="ARCH_201306" TYPE="iso9660" PTTYPE="dos"
[root@arch32-vm ~]# echo $?
0
If I remove the disk, I don't get any output and exit value is 2. (0 means success. A non-zero value will typically mean something abnormal happen or an error occurred)

[root@arch32-vm ~]# blkid /dev/sr0
[root@arch32-vm ~]# echo $?
2

Fixing slow ssh password prompt

See: http://www.doublecloud.org/2013/06/slow-ssh-client-and-quick-hack/ and: http://askubuntu.com/questions/246323/why-does-sshs-password-prompt-take-so-long-to-appear

Further searching got me a page that suggests to use –o switch in the ssh command as follows.

  1. ssh -o GSSAPIAuthentication=no [email protected]

The result is instant response for password, so the problem was solved. But I could not change the command line called by PackStack, so I had to make the change default without the switch.

To change it system wide, you can change the file in /etc/ssh folder as follows:

  1. vim /etc/ssh/ssh_config

Host *

GSSAPIAuthentication no It’s also possible to change it just for a particular user – just change the file “config” under the hidden folder .ssh of the user’s home directory. For example, you can change it using the following command for root user.

  1. vim /root/.ssh/config

Skipping GSSAPIAuthentication may have some impact on security. To find out more, check out the wiki page here.

Enable ssh access to machine, without the use of a password

From: https://okeanos.grnet.gr/support/faq/cyclades-how-can-i-add-my-public-ssh-key-in-an-existing-vm/

Generate the key pair

  1. ssh-keygen -t rsa -f autolab
  2. Then add the public key(including the second entry the '@' otherwise it wont work).
mkdir -p ~/.ssh
echo <public key contents> >> ~/.ssh/authorized_keys
chmod 0600 ~/.ssh/authorized_keys

ssh in to temporary VM without having to answer yes to adding the host key

See: http://askubuntu.com/questions/246323/why-does-sshs-password-prompt-take-so-long-to-appear

ssh -i autolab -o StrictHostKeyChecking=no 192.168.122.229

systemd

Systemctl

Preset

  • https://freedesktop.org/wiki/Software/systemd/Preset/

  • systemctl daemon-reload

    • Always run the systemctl d aemo n-rel o ad command after creating new unit files or modifying existing unit files

  • systemctl list-dependencies --after gdm.service

    • what services are ordered to start before the specified service

  • systemctl list-dependencies --before gdm.service

    • what services are ordered to start after the specified service

  • systemctl enable name.service

    • reads the [Install] section of the selected service unit and creates appropriate symbolic links to the /usr/lib/systemd/system/name.service file in the /etc/systemd /system/ directory and its subdirectories. (Does not re-create an existing link).

  • systemctl reenable name.service

  • systemctl disable name.service

  • systemctl mask name.service

    • to prevent it from being started manually or by another service.

  • systemctl unmask name.service

  • systemctl list-units --type target

  • systemctl get-default

  • systemctl list-units --type target [--all]

  • systemctl show name.service [-p PARM]

  • systemd -delta

  • Target units

Content of the unit.service file

http://www.dsm.fordham.edu/cgi-bin/man-cgi.pl?topic=systemd.unit&ampsect=5

  • [Unit]
    • After: Start this unit(defined by this file) to start after the units give in the after list.
      • What happens if a unit in the 'After=' list isn't started?
    • Before: Start this unit, before the given list of units.
    • Requires: Dont start this unit until the given unit is running, start the given unit if needed.
      • If the given unit doesn't start, then this unit isn't started.
      • If one of the other units gets deactivated or its activation fails, this unit will be deactivated.
      • If the given unit is restarted, then this unit is restarted as well(I think)
      • Note that requirement dependencies do not influence the order in which services are started or stopped. This has to be configured independently with the After= or Before= options.
    • Wants: start this unit if the given unit is running or attempted to be started.
      • If the given unit doesn't start successfully, this unit is still started.

xorp example

  1. usr/bin/systemctl preset xorp.service
  2. /usr/bin/systemctl enable xorp.service
  3. /usr/bin/systemctl start xorp

See also: http://0pointer.de/public/systemd-man/systemd.unit.html

[Unit]
Description=XORP softrouter.
After=network.target

[Service]
Type=forking
PIDFile=/var/run/xorp.pid
ExecStart=/root/xorp_bg
#ExecReload=/opt/sonar/bin/linux-x86-64/sonar.sh restart
ExecStop=/root/stop_xorp

Restart=always

[Install]
WantedBy=multi-user.target

Services

Enable rsh

NTP

NTP server

package { 'ntp': ensure => present, }

# ntpq -pn


# Disable selinux
# /etc/selinux/config

# disable the firewalld
service { 'firewalld':
  ensure => stopped,
  enable => false,
}

$szNicName="ens33"
$szServiceIpAddress="10.1.2.8"
network::if::static { "$szNicName": ensure => 'up', ipaddress => "$szServiceIpAddress", netmask => '255.255.255.0', }

# http://www.thegeekstuff.com/2014/06/linux-ntp-server-client/
# noquery prevents dumping status data from ntpd.
# notrap prevents control message trap service.
# nomodify prevents all ntpq queries that attempts to modify the server.
# nopeer prevents all packets that attempts to establish a peer association.
# Kod - Kiss-o-death packet is to be sent to reduce unwanted querie
file_line { 'ntp_conf_restrict':
  path => '/etc/ntp.conf',
  line => 'restrict default kod nomodify notrap nopeer noquery',
  match => '^restrict default',
}


file_line { 'ntp_conf_restrict_local':
  path => '/etc/ntp.conf',
  line => 'restrict 10.1.2.0 mask 255.255.255.0 nomodify notrap',
}


file_line { 'ntp_conf_server':
  path => '/etc/ntp.conf',
  line => 'server  127.127.1.0 # local clock',
  match => '^server 192.168',
}

file_line { 'ntp_conf_fudge':
  path => '/etc/ntp.conf',
  line => 'fudge   127.127.1.0 stratum 1',
}

file_line { 'ntp_conf_log':
  path => '/etc/ntp.conf',
  line => 'logfile /var/log/ntp.log',
}


service { 'ntpd':
  ensure  => running,
  enable  => true,
  require => File_line['ntp_conf_restrict','ntp_conf_server','ntp_conf_fudge','ntp_conf_log','ntp_conf_restrict_local'],
}
  • ntpq -pn
ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 127.127.1.0     .LOCL.           1 l    -   64    0    0.000    0.000   0.000

NTP client

  • Please note: If the 'receive(10.1.2.8)' is not seen, the possibly there is a firewall between the client and the server.

/usr/sbin/ntpdate -v -d -U ntp -b -p 2 10.1.2.8

 X May 10:49:36 ntpdate[XXX]: ntpdate 4.XXX@XXX XXXXXXXXX (1)
Looking for host 10.1.2.8 and service ntp
host found : 10.1.2.8
transmit(10.1.2.8)
receive(10.1.2.8)
transmit(10.1.2.8)
receive(10.1.2.8)
server 10.1.2.8, port 123
stratum 2, precision -24, leap 00, trust 000
refid [10.1.2.8], delay 0.02579, dispersion 0.00000
transmitted 2, in filter 2
reference time:    dadae999.21e6f516  Mon, May  9 2016 10:48:57.132
originate timestamp: dadae9c2.c68890b3  Mon, May  9 2016 10:49:38.775
transmit timestamp:  dadae9c2.cc6bfa06  Mon, May  9 2016 10:49:38.798
filter delay:  0.02586  0.02579  0.00000  0.00000 
         0.00000  0.00000  0.00000  0.00000 
filter offset: -0.02313 -0.02315 0.000000 0.000000
         0.000000 0.000000 0.000000 0.000000
delay 0.02579, dispersion 0.00000
offset -0.023155

 9 May 10:49:38 ntpdate[XXX]: step time server 10.1.233.88 offset -0.023155 sec

writing your own systemd services

Writing a oneshot systemd service

[Unit]
Description=execute /usr/local/bin/autoinstfromisodev.sh at start-up.
After=local-fs.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/autoinstfromisodev.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Applications

Installing Mono

Installation

Create USB for booting

  1. Download the decired ISO from Fedora project
  2. Write the .iso to the USB using gnome disk as described

There are different collections at: Fedora spins

and older .iso versions can also be found e.g. Fedora 37 ISOs

Installation on bare metal

Installation in VM

Upgrade

  1. sudo dnf upgrade --refresh
  2. sudo dnf install dnf-plugin-system-upgrade
  3. sudo dnf system-upgrade download --releasever=32
  4. sudo dnf system-upgrade reboot

Trouble shooting

troubleshooting Installation

F23 fail cp dracut

Turns out it needs 1GB RAM, and then it works.

Troubleshooting Services

ntpdate: no server suitable for synchronization found

Update the server IP addresses in both

  • /etc/ntp.conf
  • /etc/ntp/step-tickers

X

xterm Xt error: Can't open display: %s

Answer: hostname and the hostname in /etc/sysconfig/network had to be the same. the VNC server used the name from: /etc/sysconfig/network

Changed the HOSTNAME= in /etc/sysconfig/network and restarted vncserver and it worked.

:No protocol specified
Warning: This program is an suid-root program or is being run by the root user.
The full text of the error or warning message cannot be safely formatted
in this environment. You may get a more descriptive message by running the
program as a non-root user or by removing the suid bit on the executable.
xterm Xt error: Can't open display: %s