System

  Hardware | Statistics | Users | Limits | Runlevels | root password | Compile kernel |
  Repair grub | Misc
  Running kernel and system information
# uname -a                           # Get the kernel version (and BSD version)
# lsb_release -a                     # Full release info of any LSB distribution
# cat /etc/SuSE-release              # Get SuSE version
# cat /etc/debian_version            # Get Debian version

  Use /etc/DISTR-release with DISTR= lsb (Ubuntu), redhat, gentoo, mandrake, sun (Solaris),
  and so on. See also /etc/issue.
# uptime                             # Show how long the system has been running + load
# hostname                           # system's host name
# hostname -i                        # Display the IP address of the host. (Linux only)
# man hier                           # Description of the file system hierarchy
# last reboot                        # Show system reboot history

Hardware Informations

  Kernel detected hardware
# dmesg                              # Detected hardware and boot messages
# lsdev                              # information about installed hardware
# dd if=/dev/mem bs=1k skip=768 count=256 2>/dev/null | strings -n 8 # Read BIOS

Linux

# cat /proc/cpuinfo                  # CPU model
# cat /proc/meminfo                  # Hardware memory
# grep MemTotal /proc/meminfo        # Display the physical memory
# watch -n1 'cat /proc/interrupts'   # Watch changeable interrupts continuously
# free -m                            # Used and free memory (-m for MB)
# cat /proc/devices                  # Configured devices
# lspci -tv                          # Show PCI devices
# lsusb -tv                          # Show USB devices
# lshal                              # Show a list of all devices with their properties
# dmidecode                          # Show DMI/SMBIOS: hw info from the BIOS

FreeBSD

# sysctl hw.model                    # CPU model
# sysctl hw                          # Gives a lot of hardware information
# sysctl hw.ncpu                     # number of active CPUs installed
# sysctl vm                          # Memory usage
# sysctl hw.realmem                  # Hardware memory
# sysctl -a | grep mem               # Kernel memory settings and info
# sysctl dev                         # Configured devices
# pciconf -l -cv                     # Show PCI devices
# usbdevs -v                         # Show USB devices
# atacontrol list                    # Show ATA devices
# camcontrol devlist -v              # Show SCSI devices

Load, statistics and messages

  The following commands are useful to find out what is going on on the system.
# top                                # display and update the top cpu processes
# mpstat 1                           # display processors related statistics
# vmstat 2                           # display virtual memory statistics
# iostat 2                           # display I/O statistics (2 s intervals)
# systat -vmstat 1                   # BSD summary of system statistics (1 s intervals)
# systat -tcp 1                      # BSD tcp connections (try also -ip)
# systat -netstat 1                  # BSD active network connections
# systat -ifstat 1                   # BSD network traffic through active interfaces
# systat -iostat 1                   # BSD CPU and and disk throughput
# ipcs -a                            # information on System V interprocess
# tail -n 500 /var/log/messages      # Last 500 kernel/syslog messages
# tail /var/log/warn                 # System warnings messages see syslog.conf

Users

# id                                 # Show the active user id with login and group
# last                               # Show last logins on the system
# who                                # Show who is logged on the system
# groupadd admin                     # Add group "admin" and user colin (Linux/Solaris)
# useradd -c "Colin Barschel" -g admin -m colin
# usermod -a -G <group> <user>       # Add existing user to group (Debian)
# groupmod -A <user> <group>         # Add existing user to group (SuSE)
# userdel colin                      # Delete user colin (Linux/Solaris)
# adduser joe                        # FreeBSD add user joe (interactive)
# rmuser joe                         # FreeBSD delete user joe (interactive)
# pw groupadd admin                  # Use pw on FreeBSD
# pw groupmod admin -m newmember     # Add a new member to a group
# pw useradd colin -c "Colin Barschel" -g admin -m -s /bin/tcsh
# pw userdel colin; pw groupdel admin

  Encrypted passwords are stored in /etc/shadow for Linux and Solaris and /etc/master.passwd
  on FreeBSD. If the master.passwd is modified manually (say to delete a password), run #
  pwd_mkdb -p master.passwd to rebuild the database.
  To temporarily prevent logins system wide (for all users but root) use nologin. The message
  in nologin will be displayed (might not work with ssh pre-shared keys).
# echo "Sorry no login now" > /etc/nologin       # (Linux)
# echo "Sorry no login now" > /var/run/nologin   # (FreeBSD)

Limits

  Some application require higher limits on open files and sockets (like a proxy web server,
  database). The default limits are usually too low.

Linux

Per shell/script

  The shell limits are governed by ulimit. The status is checked with ulimit -a. For example
  to change the open files limit from 1024 to 10240 do:
# ulimit -n 10240                    # This is only valid within the shell

  The ulimit command can be used in a script to change the limits for the script only.

Per user/process

  Login users and applications can be configured in /etc/security/limits.conf. For example:
# cat /etc/security/limits.conf
*   hard    nproc   250              # Limit user processes
asterisk hard nofile 409600          # Limit application open files

System wide

  Kernel limits are set with sysctl. Permanent limits are set in /etc/sysctl.conf.
# sysctl -a                          # View all system limits
# sysctl fs.file-max                 # View max open files limit
# sysctl fs.file-max=102400          # Change max open files limit
# echo "1024 50000" > /proc/sys/net/ipv4/ip_local_port_range  # port range
# cat /etc/sysctl.conf
fs.file-max=102400                   # Permanent entry in sysctl.conf
# cat /proc/sys/fs/file-nr           # How many file descriptors are in use

FreeBSD

Per shell/script

  Use the command limits in csh or tcsh or as in Linux, use ulimit in an sh or bash shell.

Per user/process

  The default limits on login are set in /etc/login.conf. An unlimited value is still limited
  by the system maximal value.

System wide

  Kernel limits are also set with sysctl. Permanent limits are set in /etc/sysctl.conf or
  /boot/loader.conf. The syntax is the same as Linux but the keys are different.
# sysctl -a                          # View all system limits
# sysctl kern.maxfiles=XXXX          # maximum number of file descriptors
kern.ipc.nmbclusters=32768           # Permanent entry in /etc/sysctl.conf
kern.maxfiles=65536                  # Typical values for Squid
kern.maxfilesperproc=32768
kern.ipc.somaxconn=8192              # TCP queue. Better for apache/sendmail
# sysctl kern.openfiles              # How many file descriptors are in use
# sysctl kern.ipc.numopensockets     # How many open sockets are in use
# sysctl net.inet.ip.portrange.last=50000 # Default is 1024-5000
# netstat -m                         # network memory buffers statistics

  See The FreeBSD handbook Chapter
  11http://www.freebsd.org/handbook/configtuning-kernel-limits.html for details. And also
  FreeBSD performance
  tuninghttp://serverfault.com/questions/64356/freebsd-performance-tuning-sysctls-loader-conf
  -kernel

Solaris

  The following values in /etc/system will increase the maximum file descriptors per proc:
set rlim_fd_max = 4096               # Hard limit on file descriptors for a single proc
set rlim_fd_cur = 1024               # Soft limit on file descriptors for a single proc

Runlevels

Linux

  Once booted, the kernel starts init which then starts rc which starts all scripts belonging
  to a runlevel. The scripts are stored in /etc/init.d and are linked into /etc/rc.d/rcN.d
  with N the runlevel number.
  The default runlevel is configured in /etc/inittab. It is usually 3 or 5:
# grep default: /etc/inittab
id:3:initdefault:

  The actual runlevel can be changed with init. For example to go from 3 to 5:
# init 5                             # Enters runlevel 5
    * 0       Shutdown and halt
    * 1       Single-User mode (also S)
    * 2       Multi-user without network
    * 3       Multi-user with network
    * 5       Multi-user with X
    * 6       Reboot

  Use chkconfig to configure the programs that will be started at boot in a runlevel.
# chkconfig --list                   # List all init scripts
# chkconfig --list sshd              # Report the status of sshd
# chkconfig sshd --level 35 on       # Configure sshd for levels 3 and 5
# chkconfig sshd off                 # Disable sshd for all runlevels

  Debian and Debian based distributions like Ubuntu or Knoppix use the command update-rc.d to
  manage the runlevels scripts. Default is to start in 2,3,4 and 5 and shutdown in 0,1 and 6.
# update-rc.d sshd defaults          # Activate sshd with the default runlevels
# update-rc.d sshd start 20 2 3 4 5 . stop 20 0 1 6 .  # With explicit arguments
# update-rc.d -f sshd remove         # Disable sshd for all runlevels
# shutdown -h now (or # poweroff)    # Shutdown and halt the system

FreeBSD

  The BSD boot approach is different from the SysV, there are no runlevels. The final boot
  state (single user, with or without X) is configured in /etc/ttys. All OS scripts are
  located in /etc/rc.d/ and in /usr/local/etc/rc.d/ for third-party applications. The
  activation of the service is configured in /etc/rc.conf and /etc/rc.conf.local. The default
  behavior is configured in /etc/defaults/rc.conf. The scripts responds at least to
  start|stop|status.
# /etc/rc.d/sshd status
sshd is running as pid 552.
# shutdown now                       # Go into single-user mode
# exit                               # Go back to multi-user mode
# shutdown -p now                    # Shutdown and halt the system
# shutdown -r now                    # Reboot

  The process init can also be used to reach one of the following states level. For example #
  init 6 for reboot.
    * 0       Halt and turn the power off (signal USR2)
    * 1       Go to single-user mode (signal TERM)
    * 6       Reboot the machine (signal INT)
    * c       Block further logins (signal TSTP)
    * q       Rescan the ttys(5) file (signal HUP)

Windows

  Start and stop a service with either the service name or "service description" (shown in
  the Services Control Panel) as follows:
net stop WSearch
net start WSearch                    # start search service
net stop "Windows Search"
net start "Windows Search"           # same as above using descr.

Reset root password

Linux method 1

  At the boot loader (lilo or grub), enter the following boot option:
init=/bin/sh

  The kernel will mount the root partition and init will start the bourne shell instead of rc
  and then a runlevel. Use the command passwd at the prompt to change the password and then
  reboot. Forget the single user mode as you need the password for that.
  If, after booting, the root partition is mounted read only, remount it rw:
# mount -o remount,rw /
# passwd                             # or delete the root password (/etc/shadow)
# sync; mount -o remount,ro /        # sync before to remount read only
# reboot

FreeBSD method 1

  On FreeBSD, boot in single user mode, remount / rw and use passwd. You can select the
  single user mode on the boot menu (option 4) which is displayed for 10 seconds at startup.
  The single user mode will give you a root shell on the / partition.
# mount -u /; mount -a               # will mount / rw
# passwd
# reboot

Unixes and FreeBSD and Linux method 2

  Other Unixes might not let you go away with the simple init trick. The solution is to mount
  the root partition from an other OS (like a rescue CD) and change the password on the disk.
    * Boot a live CD or installation CD into a rescue mode which will give you a shell.
    * Find the root partition with fdisk e.g. fdisk /dev/sda
    * Mount it and use chroot:

# mount -o rw /dev/ad4s3a /mnt
# chroot /mnt                        # chroot into /mnt
# passwd
# reboot

Kernel modules

Linux

# lsmod                              # List all modules loaded in the kernel
# modprobe isdn                      # To load a module (here isdn)

FreeBSD

# kldstat                            # List all modules loaded in the kernel
# kldload crypto                     # To load a module (here crypto)

Compile Kernel

Linux

# cd /usr/src/linux
# make mrproper                      # Clean everything, including config files
# make oldconfig                     # Reuse the old .config if existent
# make menuconfig                    # or xconfig (Qt) or gconfig (GTK)
# make                               # Create a compressed kernel image
# make modules                       # Compile the modules
# make modules_install               # Install the modules
# make install                       # Install the kernel
# reboot

FreeBSD

  Optionally update the source tree (in /usr/src) with csup (as of FreeBSD 6.2 or later):
# csup <supfile>

  I use the following supfile:
*default host=cvsup5.FreeBSD.org  # www.freebsd.org/handbook/cvsup.html#CVSUP-MIRRORS
*default prefix=/usr
*default base=/var/db
*default release=cvs delete tag=RELENG_7
src-all

  To modify and rebuild the kernel, copy the generic configuration file to a new name and
  edit it as needed (you can also edit the file GENERIC directly). To restart the build after
  an interruption, add the option NO_CLEAN=YES to the make command to avoid cleaning the
  objects already build.
# cd /usr/src/sys/i386/conf/
# cp GENERIC MYKERNEL
# cd /usr/src
# make buildkernel KERNCONF=MYKERNEL
# make installkernel KERNCONF=MYKERNEL

  To rebuild the full OS:
# make buildworld                    # Build the full OS but not the kernel
# make buildkernel                   # Use KERNCONF as above if appropriate
# make installkernel
# reboot
# mergemaster -p                     # Compares only files known to be essential
# make installworld
# mergemaster -i -U                  # Update all configurations and other files
# reboot

  For small changes in the source you can use NO_CLEAN=yes to avoid rebuilding the whole
  tree.
# make buildworld NO_CLEAN=yes       # Don't delete the old objects
# make buildkernel KERNCONF=MYKERNEL NO_CLEAN=yes

Repair grub

  So you broke grub? Boot from a live cd, [find your linux partition under /dev and use fdisk
  to find the linux partion] mount the linux partition, add /proc and /dev and use
  grub-install /dev/xyz. Suppose linux lies on /dev/sda6:
# mount /dev/sda6 /mnt               # mount the linux partition on /mnt
# mount --bind /proc /mnt/proc       # mount the proc subsystem into /mnt
# mount --bind /dev /mnt/dev         # mount the devices into /mnt
# chroot /mnt                        # change root to the linux partition
# grub-install /dev/sda              # reinstall grub with your old settings

Misc

  Disable OSX virtual memory (repeat with load to re-enable). Faster system, but a little
  risky.
# sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.dynamic_pager.plist
# sleep 3600; pmset sleepnow           # go to standby in one hour (OSX)
# defaults write -g com.apple.mouse.scaling -float 8
                                    # OSX mouse acceleration (use -1 to reverse)

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