Unix - Welcome Message

Though not a big technical feature, having the right welcome message in a Unix server would be very much helpful in case of multiple server usages.

To change the welcome message modify /etc/motd file with the custom message and add update_motd="NO" line in /etc/rc.conf.

To have a custom SSH terminal welcome message create /etc/banner file with the custom message and add Banner /etc/banner line in /etc/ssh/sshd_config.

Unix - Details of the processor

# sysctl -a | egrep -i 'hw.machine|hw.model|hw.ncpu'

E.g.1:

hw.machine: i386
hw.model: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
hw.ncpu: 8
hw.machine_arch: i386

E.g.2:

hw.machine: amd64
hw.model: Intel(R) Pentium(R) D CPU 3.00GHz
hw.ncpu: 2
hw.machine_arch: amd64

Note: 'amd64' does not mean AMD processor, but 64 bit operating system.

# dmesg | grep -i cpu

E.g.1:

CPU: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz (3392.32-MHz 686-class CPU)
FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs
 cpu0 (BSP): APIC ID:  0
 cpu1 (AP): APIC ID:  1
 cpu2 (AP): APIC ID:  2
 cpu3 (AP): APIC ID:  3
 cpu4 (AP): APIC ID:  4
 cpu5 (AP): APIC ID:  5
 cpu6 (AP): APIC ID:  6
 cpu7 (AP): APIC ID:  7
cpu0: on acpi0
cpu1: on acpi0
cpu2: on acpi0
cpu3: on acpi0
cpu4: on acpi0
cpu5: on acpi0
cpu6: on acpi0
cpu7: on acpi0
est0: on cpu0
p4tcc0: on cpu0
est1: on cpu1
p4tcc1: on cpu1
est2: on cpu2
p4tcc2: on cpu2
est3: on cpu3
p4tcc3: on cpu3
est4: on cpu4
p4tcc4: on cpu4
est5: on cpu5
p4tcc5: on cpu5
est6: on cpu6
p4tcc6: on cpu6
est7: on cpu7
p4tcc7: on cpu7
SMP: AP CPU #1 Launched!
SMP: AP CPU #6 Launched!
SMP: AP CPU #3 Launched!
SMP: AP CPU #2 Launched!
SMP: AP CPU #7 Launched!
SMP: AP CPU #4 Launched!
SMP: AP CPU #5 Launched!
 

E.g.2:

CPU: Intel(R) Pentium(R) D CPU 3.00GHz (3000.17-MHz K8-class CPU)
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
 cpu0 (BSP): APIC ID:  0
 cpu1 (AP): APIC ID:  1
cpu0: on acpi0
cpu1: on acpi0
est0: on cpu0
est: CPU supports Enhanced Speedstep, but is not recognized.
est: cpu_vendor GenuineIntel, msr f2500000f25
p4tcc0: on cpu0
est1: on cpu1
est: CPU supports Enhanced Speedstep, but is not recognized.
est: cpu_vendor GenuineIntel, msr f2500000f25
p4tcc1: on cpu1
SMP: AP CPU #1 Launched!

 

# grep -i cpu /var/run/dmesg.boot

(Mostly the same output as above)

# sysctl -a | grep -i cpu | less

kern.ccpu: 0
  0, 1, 2, 3, 4, 5, 6, 7
    0, 1, 2, 3, 4, 5, 6, 7
      0, 1
      2, 3
      4, 5
      6, 7
kern.smp.cpus: 8
kern.smp.maxcpus: 32
debug.cpufreq.verbose: 0
debug.cpufreq.lowest: 0
debug.kdb.stop_cpus: 1
debug.PMAP1changedcpu: 1866
hw.model: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
hw.ncpu: 8
hw.acpi.cpu.cx_lowest: C1
machdep.hlt_cpus: 0
security.jail.param.cpuset.id: 0
dev.cpu.0.%desc: ACPI CPU
dev.cpu.0.%driver: cpu
dev.cpu.0.%location: handle=\_PR_.CPU0
dev.cpu.0.%pnpinfo: _HID=none _UID=0
dev.cpu.0.%parent: acpi0
dev.cpu.0.freq: 3401
dev.cpu.0.freq_levels: 3401/95000 3000/79831 2800/72677 2600/65779 2400/59147 2200/52789 2000/46677 1800/40818 1600/35981 1400/31483 1200/26985 1000/22488 800/17990 600/13492 400/8995 200/4497
dev.cpu.0.cx_supported: C1/1 C2/80 C3/104
dev.cpu.0.cx_lowest: C1
dev.cpu.0.cx_usage: 100.00% 0.00% 0.00% last 500us

dev.acpi_perf.0.%parent: cpu0
dev.est.0.%parent: cpu0

dev.cpufreq.0.%driver: cpufreq

dev.cpufreq.0.%parent: cpu0
dev.p4tcc.0.%desc: CPU Frequency Thermal Control
dev.p4tcc.0.%parent: cpu0
... (similar outputs for each processor in the system)

Note:

• Some outputs like hw architecture are not correct, do not give actual platform details, and are operating system dependent. For example, 'FreeBSD amd64' is generally installed on Intel i386 based platforms if 64 bit operation is expected.
• Similar is the ‘uname –p’ command. It returns the OS choice, not the actual hardware platform.

Unix - Symbolic links

A symbolic link or soft link is very much like a shortcut in Windows. Unlike a hard link, a symbolic link does not contain the data in the target file, and instead points to another file in the system.

• Let's create a hard link of new directory as the source file
  # mkdir /usr/test
  


• Let's create a symbolic link  
  # ln -s /usr/test/ /test        ( # ln –s sourceFile symbolicLinkFile )
  


• # ls –al /
  …
  lrwxr-xr-x   1 root  wheel       10 Sep 25 11:18     test -> /usr/test/
  …
  


• # touch /usr/test/sample.txt
  


• # ls /test
  sample.txt
  
  Note: sample.txt IS listed.
  


• # ls -al /test
  lrwxr-xr-x  1 root  wheel  10 Sep 25 11:18 /test -> /usr/test/
  
  Note: sample.txt IS NOT listed during detailed listing.
  


• # ls -al /usr/test/
  total 6
  drwxr-xr-x   2 root  wheel  512 Sep 25 11:21 .
  drwxr-xr-x  18 root  wheel  512 Sep 25 11:18 ..
  -rwxr-xr-x   1 root  wheel   61 Sep 25 11:22 sample.txt
  


• # touch /test/sample2.txt
  


• # ls -al /test
  lrwxr-xr-x  1 root  wheel  10 Sep 25 11:18 /test -> /usr/test/
  
  Note: sample2.txt is NOT listed either.
  


• # ls /test
  sample.txt       sample2.txt
  


• # rm /test
  
  Note: Symbolic link is deleted without any complain about files within directory
  


• # ls /usr/test/
  sample.txt       sample2.txt
  


• # rm /usr/test
  rm: /usr/test: is a directory

Unix - Z File System (ZFS)

The Z file system (ZFS) developed by Sun Microsystems is a feature rich file system for server solutions. It is designed for high storage volumes, mirror and RAID options for redundancy, data snapshots, integrity checking, and automatic repairs.

Here are some ZFS troubleshooting commands and typical outputs:

• # zpool status
  

    pool: zroot
   state: ONLINE
    scan: resilvered 30.6M in 0h0m with 0 errors on Sep 16 10:18:02 2013
  config:
  
   NAME        STATE     READ WRITE CKSUM
   zroot       ONLINE       0     0     0
     mirror-0  ONLINE       0     0     0
     gpt/disk0 ONLINE       0     0     0
     gpt/disk1 ONLINE       0     0     3
  
  errors: No known data errors 



• # zpool list
  

  NAME    SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
  zroot   228G   124G   104G    54%  1.00x  ONLINE  - 



• # zfs list
  

  NAME                        USED  AVAIL  REFER  MOUNTPOINT
  zroot                      31.8G   417G    31K  /zroot
  zroot/ROOT                 3.38G   417G  3.38G  /
  zroot/scratch              4.94G   417G  4.94G  /scratch
  zroot/tmp                  58.9M   417G  58.9M  /tmp
  zroot/usr                  21.0G   417G    31K  /usr
  zroot/usr/home             17.9G   417G  17.9G  /usr/home
  zroot/usr/local             813M   417G   813M  /usr/local
  zroot/usr/obj               997M   417G   997M  /usr/obj
  zroot/usr/ports             965M   417G   896M  /usr/ports
  zroot/usr/ports/distfiles  67.6M   417G  67.6M  /usr/ports/distfiles
  zroot/usr/ports/packages   1.30M   417G  1.30M  /usr/ports/packages
  zroot/usr/src               359M   417G   359M  /usr/src
  zroot/var                  2.46G   417G   109M  /var
  zroot/var/crash            2.15G   417G  2.15G  /var/crash
  zroot/var/db                206M   417G   204M  /var/db
  zroot/var/db/pkg           1.90M   417G  1.90M  /var/db/pkg
  zroot/var/empty              31K   417G    31K  /var/empty
  zroot/var/log               706K   417G   706K  /var/log
  zroot/var/mail             59.5K   417G  59.5K  /var/mail
  zroot/var/run              56.5K   417G  56.5K  /var/run
  zroot/var/tmp              1.79M   417G  1.79M  /var/tmp
  



• # ls -l /etc/zfs
  

  total 1
  -rw-------  1 root  wheel  181 Jun 10 12:59 exports



• # ls -l /boot/zfs /boot/zfsboot /boot/zfsloader
  

  -r--r--r--  1 root  wheel   66048 Dec  4  2012 /boot/zfsboot
  -r-xr-xr-x  1 root  wheel  303104 Oct 16  2013 /boot/zfsloader
  
  /boot/zfs:
  total 3
  -rw-r--r--  1 root  wheel  1588 Sep 13  2013 zpool.cache



• # ls -l /boot/gptboot /boot/gptzfsboot
  

  -r--r--r--  1 root  wheel  16723 Dec  4  2012 /boot/gptboot
  -r--r--r--  1 root  wheel  43443 Dec  4  2012 /boot/gptzfsboot

Unix - Hardware Timer Selection

• To find the timer counter being used by the computer:
  
  myhost# sysctl kern.timecounter.hardware
  kern.timecounter.hardware: HPET



• List of available timers:
  
  myhost# sysctl kern.timecounter.choice
  kern.timecounter.choice: TSC(-100) HPET(900)

The integer value within brackets defines the quality of the time counter compared to others. A negative value means this time counter is broken and should not be used.



• Selecting the timer of your choice:
  myhost# sysctl kern.timecounter.hardware=TSC
  
  Note: This selection does not persist after a reboot. To make this change persistent add the following line to the file /etc/sysctl.conf:
  sysctl kern.timecounter.hardware=HPET

Network Troubleshooting Commands

The following are the basic commands that helps to locate network issues. To open the command line interface or consoles:
* Ubuntu : 'Ctrl + Alt + T'
* Windows Systems : 'Window key + R' --> type 'cmd' and click 'OK/Run'


ifconfig / ipconfig

It is generally the very first to check whether the computer's network interface has got a valid IP address to establish communication with other devices in the network. MAC (physical) address of the network can also be found using these commands.

On Unix based systems,

e.g.1: ifconfig ==> Displays all the network interfaces, such as Ethernet and Loopback, MAC addresses, IP addresses, and subnet masks. Depending on the flavour of Unix and type of interface, some additional details such as number of packets transmitted and received, errors, active/disabled status, and size of the maximum transmittable unit (MTU) can also be found.

e.g.2: ifconfig eth0 down ==> Disables the Ethernet interface 'eth0'. Super user (root) only.

e.g.3: ifconfig eth0 up ==> Enables the Ethernet interface 'eth0'. Super user (root) only.

e.g.4: ifconfig eth0 192.168.1.1 netmask 255.255.255.0 ==> Assigns IP address and netmask manually. Super user (root) only.

On Windows systems,

e.g.1: ipconfig ==> Displays the IP address, netmask, and default gateway of all the network interfaces.

e.g.2: ipconfig /all ==> Displays more information about the network interfaces, including MAC address, DHCP status, and DNS servers used.

e.g.3: ipconfig /renew ==> Re-establishes TCP/IP connections on all network adapters and refreshes IP address with the DHCP server.

e.g.4: ipconfig /flushdns ==> Flushes the DNS cache stored locally (URL to IP address conversion)


ping

It is the basic command to check network reachability based on echos received from a network interface. It works in both Unix and Windows systems. However, command switches for a given additional option, such continuous ping, may vary.

On both Unix and Windows based systems,

e.g.1: ping 127.0.0.1 ==> reveals whether the IP protocol is up on you own computer (localhost). On Unix, continuously sends echo requests until terminated with 'Ctrl + C'.

e.g.2: ping www.yahoo.com ==> shows whether you can reach yahoo.com's server over the internet

On Windows,

e.g.1: ping -t www.google.com ==> On windows, continuously sends echo requests until terminated with 'Ctrl + C'.

Note:

• If no response for a well known server, then ping to the gateway IP addess found from the ifconfig / ipconfig command above. This reveals the connectivity to your network gateway.
• When URL is used with the ping command instead of an IP address, and it does not get resolved into an IP address, then the Domain Name System (DNS) resolution could be tested. 

traceroute / tracert

A command to identify the hops in the network, and in case of failures the output indicates the intermediate hops which packets travel successfully.

On Unix based systems,

e.g.1: traceroute www.yahoo.com ==> Names of hops along the network path and time taken to receive an echo response from them

On Windows, 

e.g.1: tracert www.yahoo.com ==> Names of hops along the network path and time taken to receive an echo response from them


nslookup

Returns the corresponding IP address for a given URL (also vice-versa).

On both Unix and Windows based systems,

e.g.1: nslookup www.yahoo.com 


netstat

A command to visualize the details of the ongoing network communication.

On both Unix and Windows based systems,

e.g.1: netstat ==> Details of all the established TCP connections

e.g.2: netstat -r ==> The routing table of your computer, including the default route and gateway details.


arp

Displays the IP address to MAC address conversion, and vice versa.

e.g.1: arp -a ==> Displays all the IP addresses and corresponding MAC addresses of the known network interfaces in the local broadcast domain


hostname

Gives the name assigned to your computer.

e.g.1: hostname ==> Hostname of your system


whoami / set U

Reveals the username currently used by you.

On Unix systems:

e.g.1: whoami ==> Shows your username (or 'root' in the case of superuser)

On Windows systems,

e.g.2: set U ==> Shows your username, domain, and user profile location.

IPv4 Martian Addresses

Martian addresses are the blocks of IPv4 addresses that are reserved for special use by the Internet Assigned Numbers Authority (IANA), and are NOT meant to be reached over the Internet. The following are the IANA reserved category addresses which are generally considered as Martian addresses:

Address block	Use
0.0.0.0/8	"This" network
100.64.0.0/10	Carrier-grade NAT
127.0.0.0/8	Loopback
169.254.0.0/16	Link local
192.0.0.0/24	IETF protocol assignments
192.0.2.0/24	TEST-NET-1
198.18.0.0/15	Network interconnect device benchmark testing
198.51.100.0/24	TEST-NET-2
203.0.113.0/24	TEST-NET-3
224.0.0.0/4	Multicast
240.0.0.0/4	Reserved for future use

Depending on the manufacturer of routers used at the customer premises or at the network service providers end these Martian addresses may also be blocked within Layer 3 Virtual Private Networks (IP VPNs) or Local Area Networks (LANs). E.g., Juniper Network routers block Martian addresses within IP VPNs.

Private Network IP Address Blocks

IP address blocks that are dedicated for private LANs are also included within the Martian Address blocks according to some definitions.

Subnet Address block	Use
10.0.0.0/8	Class A private networks (used as /8 subnets)
172.16.0.0/12	Class B private networks (used as /16 subnets)
192.168.0.0/16	Class C private networks (used as /24 subnets)

Bogon IP Address Blocks

IP address blocks that are yet to be allocated to any user or delegated to any regulator agency by the IANA are called Bogon IP addresses. These blocks change with time.

Unix - SSH/SCP

• Check SSH server running:
  

  # cat /etc/rc.conf | grep ssh
  sshd_enable="YES"



• SSH access to a remote machine:
  

  #/$ ssh username@remoteMachine

  
  'remoteMachine' is the DNS resolvable hostname of the remote host. IP address can also be used instead of the remote machine's hostname.


• Securely transfer file over SSH:
  

  #/$ scp -q -C -l 80000 username@remoteMachine:/home/username/test.txt \

  /home/username/. 



• Enable root access over SSH (only if it is essential):
  

  # vi /etc/ssh/sshd_config
  PermitRootLogin yes
  
  # service sshd restart  (or, # /etc/rc.d/sshd restart) 



• Generate and copy SSH keys:
  

  #/$ cd ~
  #/$ ssh-keygen -t rsa
  #/$ scp ~/.ssh/id_rsa.pub remoteMachine:.ssh/authorized_keys 

  
  'RSA' is used here as authentication mechanism. Similarly 'DSA' can also be used.


• Verify whether SSH key is working:
  

  #/$ ssh remoteMachine hostname

  
  Displays remote machine's hostname without a password prompt.


• Monitoring/tracing SSH/SCP activities:
  

  # cat /var/log/auth.log

  Displays detailed log.

Note: Unix commands and file locations used here have been tested on FreeBSD systems.

Crimping an Ethernet LAN cable

Steps:

1. Insert the cat 5e/6 cable into the boot/cap.
2. Remove approximately 1 inch of the sleeve of the wire.
3. Straighten the wires (ie, untwist the twisted pairs).
4. Arrange the wires in the right order as shown below. Choose either (EIA/TIA 568) A or B type, and if it is a straight cable follow the colour sequence of the first image on both the ends of the cable.
5. Cutoff excess length of the wire (to make it levelled inside the RJ-45 clip).
6. Insert the wire into the RJ-45 clip while maintaining the order of the wires all the way in until you can see all the wires touching on the right side wall of the clip as shown by the red line (ie, you have to insert the beyond the end of arrows shown here.)
7. Crimp the RJ-45 clip firmly with the crimping tool.
8. Fix the boot.

Unix - Memory and Disk Usages

• Statistics of process, virtual memory, disk, trap and cpu activity:
  
  # vmstat -m
  
  

           Type InUse MemUse HighUse Requests  Size(s)
         USBdev    32     3K       -       50  32,64,128,256,2048
            USB    56    18K       -       95  16,32,64,128,512,2048,4096
         isadev    10     1K       -       10  64
       ppbusdev     3     1K       -        3  128
           cdev     7     1K       -        7  128
        entropy  1024    64K       -     1024  64
          sigio     1     1K       -        1  32
       filedesc    46    12K       -   291905  16,32,256,512,2048
        kdtrace   248    54K       -   273670  64,256
           kenv    83     7K       -       92  16,32,64,128,4096
  ...
  



• Swap memory usage
  
  # swapinfo
  
  

  Device          1K-blocks     Used    Avail Capacity
  /dev/ada0p3       4194304      424  4193880     0%



• Top processes on the system
  
  # top -d1
  
  

  last pid: 73598;  load averages:  0.00,  0.00,  0.00                                                                           
  26 processes:  1 running, 25 sleeping
  CPU:     % user,     % nice,     % system,     % interrupt,     % idle
  Mem: 114M Active, 1683M Inact, 234M Wired, 121M Cache, 91M Buf, 843M Free
  Swap: 4096M Total, 424K Used, 4095M Free
  
    PID USER  THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU COMMAND
   1130 root    1  20    0 11296K  2944K select  0   0:39  0.00% sendmail
   1137 root    1  20    0  9584K  1380K nanslp  0   0:10  0.00% cron
   1003 root    1  20    0  9544K  1300K select  1   0:05  0.00% syslogd
  70226 vijay   1  20    0 15852K  4200K select  1   0:03  0.00% sshd
  70186 root    1  20    0 15852K  3992K select  0   0:03  0.00% sshd
    928 root    1  29    0  9544K  1364K select  0   0:02  0.00% dhclient
    966 _dhcp   1  20    0  9544K  1408K select  1   0:01  0.00% dhclient
    813 root    1  20    0 12132K  2868K select  1   0:01  0.00% devd
   1133 smmsp   1  20    0 11296K  2816K pause   1   0:01  0.00% sendmail
  71182 root    1  20    0 11256K  2940K select  1   0:01  0.00% ntpd
  70223 root    1  20    0 15852K  4056K select  1   0:00  0.00% sshd
   1127 root    1  20    0 13096K  3148K select  1   0:00  0.00% sshd
  70189 root    1  20    0 10864K  3188K pause   0   0:00  0.00% csh
   1183 root    1  20   -4 10092K  1868K ttyin   1   0:00  0.00% login
  73598 root    1  20    0  9872K  2008K CPU1    1   0:00  0.00% top
   1185 root    1  52    0  9544K  1240K ttyin   1   0:00  0.00% getty
   1187 root    1  52    0  9544K  1240K ttyin   1   0:00  0.00% getty
   1189 root    1  52    0  9544K  1240K ttyin   0   0:00  0.00% getty
   1188 root    1  52    0  9544K  1240K ttyin   0   0:00  0.00% getty
  ...
  



• Finding size of folders (total size of files and subfolders underneath)
  
  
  • # du –sh myfolder
  
  
  • # du –sh * => Size of all the folders in the current directory
  
  
  • # du –sk | sort –n => Size of folders, sorted by size (k  kilo byte. h gives false sorting results)
  
  

IPv4 Address Classes

Though Classless Inter-Domain Routing (CIDR) and Variable-Length Subnet Mask (VLSM) are the order of today's IPv4 networking, classification of IPv4 address spaces into classes A, B, C, or D remains common. The following table shows the classes that were designated during the days of classful routing:

Class	First bits	Address range	Subnet mask
Class A	0	1.x.x.x ~ 127.x.x.x	255.0.0.0 (/8)
Class B	10	128.0.x.x ~ 191.255.x.x	255.255.0.0 (/16)
Class C	110	192.0.0.x ~ 223.255.255.x	255.255.255.0 (/24)
Class D	1110	224.0.0.0 ~ 239.255.255.255	-
Class E	1111	240.0.0.0 ~ 255.255.255.254	-

Unix - Disk Management

Identifying the harddisks installed

• Listing all the disks and drives attached to the system
  
  

  # camcontrol devlist    (or, atacontrol list)
  
  at scbus2 target 0 lun 0 (ada0,pass0)
  at scbus3 target 0 lun 0 (cd0,pass1)



• Listing harddisks detected during the system bootup
  
  

  # dmesg | grep ad 
  
  ada0 at ata4 bus 0 scbus2 target 0 lun 0
  ada0:  ATA-8 SATA 2.x device
  ada0: 300.000MB/s transfers (SATA 2.x, UDMA5, PIO 8192bytes)
  ada0: 238418MB (488281250 512 byte sectors: 16H 63S/T 16383C)
  ada0: Previously was known as ad4
  Trying to mount root from ufs:/dev/ada0p2 [rw]...



• Listing harddisks and their partitions
  
  

  # ls /dev | grep ad
  
  ad4
  ad4p1
  ad4p2
  ad4p3
  ada0
  ada0p1
  ada0p2
  ada0p3



• Listing hardware level information of a harddisks
  
  

  # diskinfo -c ada0
  ada0
     512             # sectorsize
     250000000000    # mediasize in bytes (232G)
     488281250       # mediasize in sectors
     0               # stripesize
     0               # stripeoffset
     484406          # Cylinders according to firmware.
     16              # Heads according to firmware.
     63              # Sectors according to firmware.
     WD-WMAV12345678 # Disk ident.
  
  I/O command overhead:
     time to read 10MB block      0.124816 sec = 0.006 msec/sector
     time to read 20480 sectors   2.126440 sec = 0.104 msec/sector
     calculated command overhead               = 0.098 msec/sector
  



• #fdisk ada0
  
  

  ******* Working on device /dev/ada0 *******
  parameters extracted from in-core disklabel are:
  cylinders=484521 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Figures below won't work with BIOS for partitions not in cyl 1
  parameters to be used for BIOS calculations are:
  cylinders=484521 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Media sector size is 512
  Warning: BIOS sector numbering starts with sector 1
  Information from DOS bootblock is:
  The data for partition 1 is:
  sysid 238 (0xee),(EFI GPT)
      start 1, size 488397167 (238475 Meg), flag 80 (active)
   beg: cyl 0/ head 1/ sector 1;
   end: cyl 1023/ head 255/ sector 63
  

Identifying the harddisk partitions

• Identifying basic information about harddisk partitions
  
  

  # gpart show
  
  =>       34  488281183  ada0  GPT  (232G)
           34        128     1  freebsd-boot  (64k)
          162  478150528     2  freebsd-ufs  (228G)
    478150690    8388608     3  freebsd-swap  (4.0G)
    486539298    1741919        - free -  (850M)
  



• Displaying detailed information of harddisk partitions
  
  

  # gpart list
  
  Geom name: ada0
  modified: false
  state: OK
  fwheads: 16
  fwsectors: 63
  last: 488281216
  first: 34
  entries: 128
  scheme: GPT
  Providers:
  1. Name: ada0p1
     Mediasize: 65536 (64k)
     Sectorsize: 512
     Stripesize: 0
     Stripeoffset: 17408
     Mode: r0w0e0
     rawuuid: 740aff84-9a1e-11e3-b778-002219173177
     rawtype: 83bd6b9d-7f41-11dc-be0b-001560b84f0f
     label: (null)
     length: 65536
     offset: 17408
     type: freebsd-boot
     index: 1
     end: 161
     start: 34
  2. Name: ada0p2
     Mediasize: 244813070336 (228G)
     Sectorsize: 512
     Stripesize: 0
     Stripeoffset: 82944
     Mode: r1w1e1
     rawuuid: 740b80b0-9a1e-11e3-b778-002219173177
     rawtype: 516e7cb6-6ecf-11d6-8ff8-00022d09712b
     label: (null)
     length: 244813070336
     offset: 82944
     type: freebsd-ufs
     index: 2
     end: 478150689
     start: 162
  3. Name: ada0p3
     Mediasize: 4294967296 (4.0G)
     Sectorsize: 512
     Stripesize: 0
     Stripeoffset: 17408
     Mode: r1w1e0
     rawuuid: 740eaebd-9a1e-11e3-b778-002219173177
     rawtype: 516e7cb5-6ecf-11d6-8ff8-00022d09712b
     label: (null)
     length: 4294967296
     offset: 244813153280
     type: freebsd-swap
     index: 3
     end: 486539297
     start: 478150690
  Consumers:
  1. Name: ada0
     Mediasize: 250000000000 (232G)
     Sectorsize: 512
     Mode: r2w2e3
  




• df -h
  
  Filesystem      Size    Used   Avail Capacity  Mounted on
  /dev/ada0p2     220G    7.6G    195G     4%    /
  devfs           1.0k    1.0k      0B   100%    /dev
  nfsServer:/home 435G     15G    420G     3%    /usr/home
  

Mounting and unmounting external drives

For a USB memory stick,

• # mount -t msdosfs /dev/da0s1 /tmp/usb
• # umount /tmp/usb

While inserting a USB memory stick, a notification on the console will indicate the new device location like /dev/da0. But, you have to find the active partition of the drive like /dev/da0s1 to mount (# ls /dev | grep da could be used).


Note: Unix commands and file locations used here have been tested on FreeBSD systems.

Unix - File Access Rights and Ownerships

File Attributes

#/$ ls -l /tmp
drwxr-xr-x  4 vijay  wheel           10 Apr 16  2010 testFolder
-rw-r--r--  2 vijay  wheel       368884 Feb 13  2012 news.txt
-rwx------  2 vijay  wheel         2687 Feb 13  2012 secret.txt
-rwxr-xr-x  2 vijay  wheel        11762 Nov 10  2011 code.c

Symbolic permissions

Option	Letter	Represents
(who)	u	User
(who)	g	Group owner
(who)	o	Other
(who)	a	All (“world”)
(action)	+	Adding permissions
(action)	-	Removing permissions
(action)	=	Explicitly set permissions
(permissions)	r	Read
(permissions)	w	Write
(permissions)	x	Execute
(permissions)	t	Sticky bit
(permissions)	s	Set UID or GID

To modify the access rights, modify the file attributes.

# chmod 777 testfile	Allows access by File Owner, Group Members, and All-other-users.
# chmod –R 755 /tmp/test/	-R affects access rights all the files and sub-folders in /tmp/test/
# chmod go= testfile	Symbolic permission (who) (action) (permissions)
# chmod go-w,a+x testfile

Extended file attributes

# getfacl testfile
# setfacl -k testfile
# setfacl -m u:trhodes:rwx,group:web:r--,o::--- testfile

setuid (4), setgid (2), and sticky (1) permissions

# chmod 4755 testfile
=> File will always use permissions and the same user ID of who assigned it)
-rwsr-xr-x (x of owner is replaced with s)

# chmod 2755 testfile
=> File will always use permissions of the group (of the group to assigner belongs)
-rwxr-sr-x (x of group is replaced with s)

# chmod 1777 testdir
=> Allows file deletion only by the owner (make sense for directories)
drwxrwxrwt (x of all-users is replaced with t)

File flags (FreeBSD specific)

File flags are used to prevent accidental editing/removal of files (non-directory) by the root and/or the file owners in FreeBSD.

To view them:

# ls -lo /etc | grep rc.conf
-rw-r--r--  1 root  wheel  schg 1897 Mar  1 2012  rc.conf

In the above case, the secret tool 'schg' makes the file rc.conf unmodifiable even by the superuser (root) without removing the flag. This feature provides one additional level of protection for important files from accidental modifications by the system administrator(s).

Super user (root) only assignable flags

• sappnd, sappend : sets the system append-only flag (by super-user only)
• sunlnk, sunlink : sets the system undeletable flag (by super-user only)
• schg, schange, simmutable : sets the system immutable flag (by super-user only)

Normal user assignable flags

• uappnd, uappend : sets the user append-only flag (by owner or super-user only)
• uunlnk, uunlink : sets the user undeletable flag (by owner or super-user only)
• uchg, uchange, uimmutable : sets the user immutable flag (by owner or super-user only)

To edit these flags chflags command is used. For example:

# chflags sunlink testfile   => Undeletable
# chflags nosunlink testfile

# chflags schg httpd.conf  => System immutable (no change) flag
# chflags noschg httpd.conf

File Ownership

To change the file ownership:
# chown –R vijay:wheel *

Note: Unix commands and file locations used here have been tested on FreeBSD systems.

Unix - DHCP

After addition of a new network interface card (NIC) in a DHCP client and/or changing cable from one port to another, client might not establish the network connectivity. In such cases first check whether the active NIC's MAC address is there on DHCP server's database. If it is not there then add the MAC address and restart the server. If the problem persists, refresh the DHCP client as below:

# service netif restart

# dhclient eth1