Linux useful one liners

File operations

Search directory for large files (larger than 2GB) and show 10 largest
find Desktop/ -size +2G | xargs ls -l | sort +4nr -5 | head -n 10
+   larger than
-    smaller than
c   bytes
k   Kilobytes
M  Megabytes
G   Gigabytes

Empty log file:
truncate -s 0 messages

truncate command makes the specified file of a needed size, if size (-s option) is zero, then the file will be empty. 

Find how many times the specified Asterisk SIP extension was unreachable:

grep -Ei "9011.+unreachable" /var/log/asterisk/messages | awk '{split($1,month,"[");  printf " %s %s %s  %s\n", month[2], $2, $7, $10}' | sort -k 2 | uniq -c
      1   Jan 10 '9011'  UNREACHABLE!
     10  Jan 11 '9011'  UNREACHABLE!
      2   Jan 12 '9011'  UNREACHABLE!
      1   Jan 16 '9011'  UNREACHABLE!
     18  Jan 18 '9011'  UNREACHABLE!
      1  Dec 28 '9011'  UNREACHABLE!
      4  Dec 29 '9011'  UNREACHABLE!
      2  Dec 30 '9011'  UNREACHABLE!
      6  Jan 6 '9011'  UNREACHABLE!
      1  Jan 9 '9011'  UNREACHABLE!

Create asterisk dump file
From asterisk server shell:
tcpdump -w - -p -n -s 0 udp > /tmp/cli-capture.pcap
-w = output file
-p = don't start in promiscuous mode
-n = no name resolution
-s 0 = full frame, not only first bytes
udp = only capture udp packets

Then upload pcap file and analyze with Wireshark.

Network Related

View NIC parameters
ethtool eth4
Settings for eth4:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  Not reported
    Advertised pause frame use: No
    Advertised auto-negotiation: Yes
    Speed: 100Mb/s
    Duplex: Full
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    MDI-X: Unknown
    Supports Wake-on: pg
    Wake-on: d
    Current message level: 0x0000003f (63)
                   drv probe link timer ifdown ifup
    Link detected: yes

Find needed NIC port
sometimes we can't find needed Ethernet NIC port of the rack server, we can use ethtool to make NIC blinking for specified amount of seconds:
ethtool -p eth4 15

Getting Server Info

Vendor, Model, Serial:
dmidecode -t 1 | grep "Manuf\|Product\|Serial"

Processor Sockets & Installed Processor:

dmidecode -t 4 | grep "Processor\|Socket\|Version"

RAM slots & Installed RAM:
dmidecode -t 17 | grep "Device\|Size\|DIMM_"

HDD  info:

smartctl -a /dev/your_device_here | grep "Vendor\|Product\|Capacity"