9. System context

This section describes commands that print or change system-wide information.

9.1 date: Print or set system date and time

date with no arguments prints the current time and date, in the format of the `%c' directive (described below).

Synopses:

date [ option ]... [ +format ]
date [ -u|--utc|--universal ] 
[ MMDDhhmm[[CC]YY][.ss] ]

If given an argument that starts with a `+', date prints the current time and date (or the time and date specified by the --date option, see below) in the format defined by that argument, which is the same as in the strftime function. Except for directives, which start with `%', characters in the format string are printed unchanged. The directives are described below.

By default, date pads numeric fields with zeroes. GNU date recognizes the following numeric modifiers between the `%' and the directive. These are GNU extensions.

`-'

(hyphen) do not pad the field

`_'

(underscore) pad the field with spaces

9.1.1 Time directives

date directives related to times.

`%H'

hour (00...23)

`%I'

hour (01...12)

`%k'

hour ( 0...23)

`%l'

hour ( 1...12)

`%M'

minute (00...59)

`%p'

locale's AM or PM

`%r'

time, 12-hour (hh:mm:ss [AP]M)

`%s'

seconds since the epoch, i.e., 1 January 1970 00:00:00 UTC (a GNU extension)

`%S'

second (00...61)

`%T'

time, 24-hour (hh:mm:ss)

`%X'

locale's time representation (%H:%M:%S)

`%Z'

time zone (e.g., EDT), or nothing if no time zone is determinable

9.1.2 Date directives

date directives related to dates.

`%a'

locale's abbreviated weekday name (Sun...Sat)

`%A'

locale's full weekday name, variable length (Sunday...Saturday)

`%b'

locale's abbreviated month name (Jan...Dec)

`%B'

locale's full month name, variable length (January...December)

`%c'

locale's date and time (Sat Nov 04 12:02:33 EST 1989)

`%d'

day of month (01...31)

`%D'

date (mm/dd/yy)

`%h'

same as %b

`%j'

day of year (001...366)

`%m'

month (01...12)

`%U'

week number of year with Sunday as first day of week (00...53)

`%w'

day of week (0...6) with 0 corresponding to Sunday

`%W'

week number of year with Monday as first day of week (00...53)

`%x'

locale's date representation (mm/dd/yy)

`%y'

last two digits of year (00...99)

`%Y'

year (1970....)

9.1.3 Literal directives

date directives that produce literal strings.

`%%'

a literal %

`%n'

a newline

`%t'

a horizontal tab

9.1.4 Setting the time

If given an argument that does not start with `+', date sets the system clock to the time and date specified by that argument (as described below). You must have appropriate privileges to set the system clock. The `--date' and `--set' options may not be used with such an argument. The `--universal' option may be used with such an argument to indicate that the specified time and date are relative to Coordinated Universal Time rather than to the local time zone.

The argument must consist entirely of digits, which have the following meaning:

MM

month

DD

day within month

hh

hour

mm

minute

CC

first two digits of year (optional)

YY

last two digits of year (optional)

ss

second (optional)

The `--set' option also sets the system clock; see the next section.

9.1.5 Options for date

The program accepts the following options. Also see section 2. Common options.

`-d datestr'

`--date=datestr'

Display the time and date specified in datestr instead of the current time and date. datestr can be in almost any common format. It can contain month names, timezones, `am' and `pm', `yesterday', `ago', `next', etc. The source file `getdate.y' implements this parsing for all GNU routines; we need precise documentation!

`-f datefile'

`--file=datefile'

Parse each line in datefile as with `-d' and display the resulting time and date. If datefile is `-', use standard input. This is useful when you have many dates to process, because the system overhead of starting up the date executable many times can be considerable.

`-s datestr'

`--set=datestr'

Set the time and date to datestr, See `-d' above.

`-u'

`--utc'

`--universal'

Print or set the time and date in Universal Coordinated Time instead of in local (wall clock) time.

9.1.6 Examples of date

Here are a few examples. Also see the documentation for the `-d' option in the previous section.

• To print the date of the day before yesterday:

  date --date='2 days ago'
  

• To print the date of the day three months and one day hence:

  date --date='3 months 1 day'
  

• To print the day of year of Christmas in the current year:

  date --date='25 Dec' +%j
  

• To print the current full month name and the day of the month:

  date '+%B %d'
  

  But this may not be what you want because for the first nine days of the month, the `%d' expands to a zero-padded two-digit field, for example `date -d 1may '+%B %d'' will print `May 01'.
• To print a date without the leading zero for one-digit days of the month, you can use the (GNU extension) - modifier to suppress the padding altogether.

  date -d=1may '+%B %-d'
  

• To print the current date and time in the format required by many non-GNU versions of date when setting the system clock:

  date +%m%d%H%M%Y.%S
  

• To set the system clock forward by two minutes:

  date --set='+2 minutes'
  

9.2 uname: Print system information

uname prints information about the machine and operating system it is run on. If no options are given, uname acts as if the -s option were given.

Synopsis:

uname [ option ]...

If multiple options or -a are given, the selected information is printed in this order:

sysname nodename release osversion machine

The osversion, at least, may well be multiple words. For example:

bash$ uname -a
=> Linux hayley 1.0.4 #3 Thu May 12 18:06:34 1994 i486

The program accepts the following options. Also see section 2. Common options.

`-a'

`--all'

Print all of the below information.

`-m'

`--machine'

Print the machine (hardware) type.

`-n'

`--nodename'

Print the machine's network node hostname.

`-r'

`--release'

Print the operating system release.

`-s'

`--sysname'

Print the operating system name.

`-v'

Print the operating system version.

9.3 hostname: Print or set system name

With no arguments, hostname prints the name of the current host system. With one argument, it sets the current host name to the specified string. You must have appropriate privileges to set the host name.

Synopsis:

hostname [ name ]

The only options are `--help' and `--version'. See section 2. Common options.

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