diff --git a/src/kernel/00_preamble.lua b/src/kernel/00_preamble.lua
index 379f036..7fc5e01 100644
--- a/src/kernel/00_preamble.lua
+++ b/src/kernel/00_preamble.lua
@@ -2,16 +2,17 @@
 local bootfs = ...
 -- ...but [lua bios, openloader] don't, so fall back to the usual way
 bootfs = bootfs or computer.getBootAddress()
+local tmpfs = computer.tmpAddress()
 
 --store all functions we need in locals so userspace mischief can't replace them
 --prefix 'k' (for kernel) on any functions userspace will also have a version of to ensure kernelspace
 --function usage is intentional (ie prevent accidentally using the kernel's `load` in a userspace `loadfile`)
 local envBase = _G --used for creating process environments
 local assert, checkArg, error, kload, ipairs, next, pairs, rawequal, rawset, setmetatable, tostring, type = assert, checkArg, error, load, ipairs, next, pairs, rawequal, rawset, setmetatable, tostring, type
-local invoke = component.invoke
+local invoke, component_type = component.invoke, component.type
 local kpullSignal, shutdown, uptime = computer.pullSignal, computer.shutdown, computer.uptime
 local co_create, co_status, kresume, kyield = coroutine.create, coroutine.status, coroutine.resume, coroutine.yield
-local huge, math_type = math.huge, math.type
+local huge, math_type, random = math.huge, math.type, math.random
 local find, format, match, sub = string.find, string.format, string.match, string.sub
 local concat, pack, unpack = table.concat, table.pack, table.unpack
 
diff --git a/src/kernel/02_io.lua b/src/kernel/02_io.lua
index 771dc03..e8b4c35 100644
--- a/src/kernel/02_io.lua
+++ b/src/kernel/02_io.lua
@@ -14,14 +14,18 @@ do
 	end
 
 	local function wrapFile(mode, fh)
-		local rwa, bin, plus, b2 = match(mode or 'r', '^([rwa])(b?)(%+?)(b?)$') --match all of x, xb, x+, xb+, x+b
-		if not rwa or (bin ~= '' and b2 ~= '') then return nil, 'bad mode' end
-		bin = bin .. b2 --when (bin == '') xor (b2 == ''), this is logical or
+		local rwa, b, plus, b2 = match(mode or 'r', '^([rwa])(b?)(%+?)(b?)$') --match all of x, xb, x+, xb+, x+b
+		if not rwa or (b ~= '' and b2 ~= '') then return nil, 'bad mode' end
 
 		local read = rwa == 'r' or plus
 		local write = rwa ~= 'r' or plus
 		local append = rwa == 'a'
 		local update = plus ~= ''
+		local bin = (b .. b2) ~= ''
+
+		--TODO truncate if w+
+		--TODO restrict seeking on a
+		--TODO restrict seek to end before write on a+
 
 		local file = setmetatable({}, filemt)
 		filedata[file] = fh
@@ -50,6 +54,7 @@ do
 	local function path_seek(fh, ...) return invoke(fh.address, 'seek', fh.handle, ...) end
 
 	function openPath(mode, addr, path)
+		--TODO do filesystem components support 'a' modes?
 		local fd, err = invoke(addr, 'open', path, mode) --should we validate `mode` first?
 		if not fd then
 			return nil, err
@@ -132,9 +137,7 @@ do
 			if wbuf ~= '' then return flush(fh) end
 		elseif mode == 'full' then
 			local cap = fh._file_wcap or 512 --TODO tune default capacity to e.g. free memory
-			if #fh._file_wbuf >= cap then
-				return flush(fh)
-			end
+			if #fh._file_wbuf >= cap then return flush(fh) end
 		else --for line buffering, only flush complete lines
 			local i1, i2 = find(fh._file_wbuf, '.+[\r\n]') --`i2` is the last cr or lf in the buffer
 			if i1 then --if there are any newlines
@@ -143,10 +146,10 @@ do
 				local ok, err = flush(fh)
 				if ok then fh._file_wbuf = rest end
 				return ok, err
-			else --no newlines, nothing to flush
-				return true
 			end
 		end
+		--never hit any of the branches that `return flush(fh)`ed, so we've successfully written to the buffer
+		return true
 	end
 
 
@@ -258,7 +261,7 @@ do
 
 		local tell = (whence == 'cur' or not whence) and (offset == 0 or not offset) --true if we didn't move ie ftell()
 		--after seeking, if we moved, invalidate the read buffer
-		if (whence and whence ~= cur) or (offset and offset ~= 0) then
+		if (whence and whence ~= 'cur') or (offset and offset ~= 0) then
 			fh._file_rbuf = fh._file_rbuf and ''
 		end
 
diff --git a/src/kernel/04_environment.lua b/src/kernel/04_environment.lua
index 0b9956e..744637c 100644
--- a/src/kernel/04_environment.lua
+++ b/src/kernel/04_environment.lua
@@ -9,7 +9,7 @@ given <https://ocdoc.cil.li/tutorial:custom_oses#what_s_available>:
 ]]
 
 
-envBase._OSVERSION = 'kitn 0.2.0-beta.1' --prefer [openloader, openos] "$name $ver" over plan9k "$name/$ver"
+envBase._OSVERSION = 'kitn 0.2.0-beta.2' --prefer [openloader, openos] "$name $ver" over plan9k "$name/$ver"
 envBase.kitn = {}
 envBase._G, envBase.load = nil
 
@@ -100,7 +100,11 @@ function fillEnv(proc, uenv)
 			checkArg(1, filename, 'string', 'nil')
 			error('TODO io.lines') --iff we open a file, we need to close it
 		end,
-		open = function(filename, mode) return openPath(mode, bootfs, filename) end,
+		open = function(filename, mode)
+			checkArg(1, filename, 'string')
+			checkArg(2, filename, 'string', 'nil')
+			return openPath(mode, bootfs, filename)
+		end,
 		output = function(file)
 			local t = checkArgEx(1, file, 'string', 'table', 'nil')
 			if t ~= nil then
@@ -111,8 +115,14 @@ function fillEnv(proc, uenv)
 		--popen is unimplemented because we don't have a notion of a shell
 		read = function(...) return uio.stdin:read(...) end,
 		tmpfile = function()
-			--use math.random() to pick a filename on computer.tmpAddress() that doesn't exist yet and create it
-			error('TODO io.tmpfile') --file is deleted on process exit, requires atExit mechanism
+			local deadline = uptime() + 1 --give up after 1s instead of potentially infinitely looping
+			local filename
+			repeat
+				filename = format('tmp.%08x', random(0, 0x7fffffff))
+				if invoke(tmpfs, 'exists', filename) then filename = nil end
+			until filename or uptime() >= deadline
+			assert(filename, 'failed to allocate tmpfile')
+			return openPath('w+', tmpfs, filename) --TODO close at exit
 		end,
 		type = function(obj)
 			local file, opened = isFile(obj)
@@ -128,6 +138,14 @@ function fillEnv(proc, uenv)
 	}
 	uenv.io = uio
 
+	function uenv.print(...)
+		local parts = pack(...)
+		for i = 1, parts.n do
+			parts[i] = tostring(parts[i])
+		end
+		assert(uenv.io.write(concat(parts, '\t', 1, parts.n), '\n'))
+	end
+
 
 	--env will automatically mirror envBase.kitn here
 	local ukitn = uenv.kitn
@@ -154,6 +172,18 @@ function fillEnv(proc, uenv)
 		--TODO return information for the current thread within the process too
 		return proc, nil
 	end
+
+	--TODO map all filesystems into a single tree, then remove this method
+	function ukitn.openOn(address, path, mode)
+		checkArg(1, address, 'string')
+		checkArg(2, path, 'string')
+		checkArg(3, mode, 'string', 'nil')
+		local t, err = component_type(address)
+		if t ~= 'filesystem' then
+			return nil, err or 'component is not a filesystem'
+		end
+		return openPath(mode, address, path)
+	end
 end
 
 -- vi: set ts=2: