Thursday, November 25, 2010

Permission of authorized_keys and private key file

~/.ssh/authorized_keys: should be 600

~/.ssh/id_dsa, ~/.ssh/id_rsa: must be 600

 

If permissions are not set correctly, the login process may fail without giving any useful information!

awk/gawk notes

       
RS Record Separator single character That character separates the records.
    regular expression Text in input matches reg exp separates records.
    null string Records are separated by blank lines. The  newline character always acts as a field separator, in addition to whatever value FS may have.
NR number of records seen so far    
FNR The input record number in the current input file    
ORS output record separator    
FS Field separator single character Fields are separated by that character
    single space fields are separated by runs of spaces  and/or  tabs  and/or  newlines.
    Null string each individual character becomes a separate field.
    regular expression  
OFS output field separator    
FIELDWIDTHS   a space separated list of numbers each field is expected to have fixed width. The value  of  FS  is ignored.  Assigning a new value to FS overrides the use of FIELDWIDTHS, and restores the default behavior.
NF number of fields   Decrementing NF causes the values of fields past the new value to be lost, and the value of $0 to be recomputed
IGNORECASE Controls the case-sensitivity of all regular expression  and  string  operations. non-zero
zero
non-zero: ignore case
       
Field Reference How to reference a field $1, $2, … $NF Access a field. Assigning  a value to an existing field causes the whole record to be rebuilt when $0 is referenced.
    $-1, $-2 fatal error
    non-existent fields For read, produce null-string. For write, 1)increase NF 2) create intervening fields with null string 3) $0 is recomputed
    $0 whole record.  assigning a value to $0 causes the record to be  resplit,  creating  new values for the fields.
CONVFMT    

A number is converted to a string by using the value  of  CONVFMT  as  a  format  string  for  sprintf(3), with the numeric value of the variable as the argument.  However, even though all numbers in AWK are floating-point, integral values are always converted as  integers.

OFMT      
All arrays in AWK are associative, i.e. indexed by string values.

i = "A"; j = "B"; k = "C"
x[i, j, k] = "hello, world\n"

key is "A\034B\034C" and value is "hello, world\n". Key test: val in array. for(val in array)…