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`date(1)` on Solnix vs Linux and the BSDs

On Solnix, date is the illumos date at /usr/bin/date. It has only -a, -r, -R, -u, a +format operand and a set-time operand. Linux's -d, -s, -I and -f, FreeBSD's -v and -j, and the BSD -z do not exist, and the set-time string puts the year last, not first as on the BSDs.

The manual pages

Solnix: date(1) from pkgs.solnix.illumos-world-man · illumos.org
Linux: date(1) coreutils-full-9.11
FreeBSD: date(1) 15.1-RELEASE
OpenBSD: date(1) 8.0
NetBSD: date(1) 11.0
Standard: POSIX.1-2024 (IEEE Std 1003.1-2024), date

What Solnix runs

A default Solnix system runs the illumos /usr/bin/date. /usr/xpg4/bin/date is also shipped with the same synopsis. The documented difference is the %C conversion: /usr/bin/date gives the locale's date and time representation, while /usr/xpg4/bin/date gives the century as [00-99]. Both are marked CSI enabled.

Differences

Compared with	Topic	What differs
FreeBSD, OpenBSD, NetBSD	set-time operand order	Solnix sets the time with [mmdd]HHMM or mmddHHMM[cc]yy[.SS], with the year after the minutes. The three BSDs use [[[[[cc]yy]mm]dd]HH]MM[.SS], with the year first and the minutes required. Do not reuse a longer date string between them. Source: Solnix date(1) SYNOPSIS and OPERANDS; FreeBSD date(1) SYNOPSIS; OpenBSD date(1) DESCRIPTION, STANDARDS; NetBSD date(1) DESCRIPTION
Linux	setting and parsing free-form dates	Solnix has no `-d` and no `-s`. It sets the clock only through the positional operand and cannot parse a free-form date string. Linux `-d` STRING displays an arbitrary described time and `-s` STRING sets the time from a string. Source: Solnix date(1) SYNOPSIS, OPTIONS; Linux date(1) -d, --date; -s, --set
all four	`-f` meaning	Solnix date has no `-f`. On Linux, `-f` reads a file of date strings, one per line. On FreeBSD, OpenBSD and NetBSD, `-f` gives a strptime(3) input format for parsing the new date. The same flag means different things on Linux and the BSDs. Source: Solnix date(1) SYNOPSIS; Linux date(1) -f, --file; FreeBSD date(1) -f; OpenBSD date(1) -f; NetBSD date(1) -f
FreeBSD, OpenBSD, NetBSD	`-j` and `-z` missing	Solnix has no `-j` (parse without setting) and no `-z` (output time zone). Set TZ in the environment instead. Solnix uses TZ unless `-u` is given. NetBSD `-z` with an empty string reverts to the default zone, ignoring TZ. Source: Solnix date(1) ENVIRONMENT VARIABLES (TZ); FreeBSD date(1) -j, -z; OpenBSD date(1) -j, -z; NetBSD date(1) -z
all four	`-a` meaning	Solnix `-a` takes an argument [-]sss.fff and slowly adjusts the clock by that many seconds. OpenBSD and NetBSD `-a` takes no argument and uses adjtime(2) to skew toward the time given as the operand. Linux and FreeBSD list no `-a`. Source: Solnix date(1) -a; OpenBSD date(1) -a; NetBSD date(1) -a; Linux date(1) OPTIONS; FreeBSD date(1) OPTIONS
Linux, OpenBSD, NetBSD	`-r` meaning	Solnix `-r` accepts either epoch seconds or a filename (its modification time). FreeBSD does the same. Linux `-r` accepts only a file. OpenBSD and NetBSD `-r` accept only seconds since the Epoch. Source: Solnix date(1) -r seconds, -r filename; FreeBSD date(1) -r; Linux date(1) -r, --reference; OpenBSD date(1) -r; NetBSD date(1) -r
all four	`-R` output format	Solnix `-R` uses %a, %d %h %Y %H:%M:%S %z, described as similar to RFC 822. Linux and NetBSD describe `-R` as RFC 5322, and FreeBSD as RFC 2822. OpenBSD's date has no `-R`. Source: Solnix date(1) -R; Linux date(1) -R, --rfc-email; FreeBSD date(1) -R; NetBSD date(1) -R; OpenBSD date(1) SYNOPSIS
Linux, FreeBSD	ISO 8601 output	Solnix has no `-I`. Linux and FreeBSD `-I`[FMT] print ISO 8601 output. On Solnix, build it with a +format string. Source: Solnix date(1) SYNOPSIS; Linux date(1) -I, --iso-8601; FreeBSD date(1) -I
FreeBSD	date arithmetic with `-v`	FreeBSD `-v` adjusts the displayed date by units (y, m, w, d, H, M, S). Solnix, Linux, OpenBSD and NetBSD have no `-v`, so date arithmetic needs another tool or approach. Source: FreeBSD date(1) -v; Solnix date(1) SYNOPSIS
Linux	%C meaning	With `/usr/bin/date`, Solnix %C is the locale's date and time representation. Linux %C is the century. `/usr/xpg4/bin/date` gives the century like Linux does. Source: Solnix date(1) OPERANDS +format; Linux date(1) %C
FreeBSD, OpenBSD, NetBSD	`-n` and `-U`	Solnix has no `-n` or `-U`. FreeBSD `-n` is obsolete and ignored. NetBSD `-n` stops date setting the time on other machines when timed(8) is running. NetBSD `-U` resets the zone changed by `-u` or `-z`. Source: FreeBSD date(1) -n; NetBSD date(1) -n, -U; Solnix date(1) SYNOPSIS

Standards

POSIX: date is a POSIX.1-2024 utility.
Solnix: ATTRIBUTES: CSI is enabled for both /usr/bin/date and /usr/xpg4/bin/date.
OpenBSD: The date utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”) specification. Flags -a, -f, -j, -r, -z and several conversions are extensions. The required BSD date format differs from the X/Open System Interfaces option.
NetBSD: The date utility is expected to be compatible with IEEE Std 1003.2 (“POSIX.2”). True compatibility requires running date with POSIXLY_CORRECT set, to parse the archaic time string format POSIX demands.

Writing portable scripts

Use only -u, a +format operand and, if needed, -r seconds in portable scripts. Avoid -d, -f, -j, -z, -v, -a and -I, which differ or are missing.
Do not rely on %N, which the Solnix and Linux pages document. The BSD pages defer to strftime(3) and do not list it. Avoid setting the clock with a bare digit string in cross-system scripts, since the year position differs.

Every difference here is taken from the manual pages linked above: Solnix's published page, Linux (man-pages and the GNU and util-linux manuals), FreeBSD, OpenBSD and NetBSD. Each row names its source. Where a manual is silent, this page is too. Compiled 2026-10-26. Found a mistake? Mail hackers@lists.solnix.io.