Command line options
The command line for invoking kdb+ has the form:
q [file] [-option [parameters] … ]
Options -b blocked -q quiet mode -c console size -r replicate -C HTTP size -s secondary threads -e error traps -S random seed -E TLS Server Mode -t timer ticks -g garbage collection -T timeout -l log updates -u disable syscmds -L log sync -u usr-pwd local -m memory domain -U usr-pwd -o UTC offset -w workspace -p listening port -W start week -P display precision -z date format
This is either the script to load (*.q, *.k, *.s), or a file or a directory.
$ q sp.q KDB+ 3.5t 2017.02.28 Copyright (C) 1993-2017 Kx Systems m32/ 4()core 8192MB sjt mint.local 192.168.0.39 NONEXPIRE
+`p`city!(`p$`p1`p2`p3`p4`p5`p6`p1`p2;`london`london`london`london`london`lon.. (`s#+(,`color)!,`s#`blue`green`red)!+(,`qty)!,900 1000 1200 +`s`p`qty!(`s$`s1`s1`s1`s2`s3`s4;`p$`p1`p4`p6`p2`p2`p4;300 200 100 400 200 300) q)
Operating systems may create hidden files, such as
.DS_Store, that block loading of a directory.
Block write-access to a kdb+ database, for any handle context (
.z.w) other than 0.
~/q$ q -b
q)aa:(bb:til 4) q)\p 5001 q)
and in another task
q)h:hopen 5001 q)h"count aa" 4 q)h"aa:10#aa" 'noupdate q)
\_ to check if client write-access is blocked:
~/q$ q -b .. q)\_ 1
-c (console size)
-c r c
Set console maximum rows and columns, default 25 80.
\c system command for detail
-C (HTTP size)
-C r c
Set HTTP display maximum rows and columns.
\C system command for detail
-e (error traps)
Sets error-trapping mode. The default is 0 (off).
\e system command for detail
-E (TLS Server Mode)
-E 0 / plain -E 1 / plain & TLS -E 2 / TLS only
-g (garbage collection)
-g 0 / deferred (default) -g 1 / immediate
Sets garbage-collection mode.
\g system command for detail
-l (log updates)
Log updates to filesystem.
-L (log sync)
-l, but sync logging.
Memory can be backed by a filesystem, allowing use of DAX-enabled filesystems (e.g. AppDirect) as a non-persistent memory extension for kdb+.
This command-line option directs kdb+ to use the filesystem path specified as a separate memory domain. This splits every thread’s heap into two:
domain description -------------------------------------------------------------------------- 0 regular anonymous memory, active and used for all allocs by default 1 filesystem-backed memory
.m namespace is reserved for objects in memory domain 1, however names from other namespaces can reference them too, e.g.
a:.m.a:1 2 3
-o (UTC offset)
Sets local time offset as
N hours from UTC, or minutes if
\o system command for detail
-p (listening port)
Set listening port
See Listening port for detail.
-P (display precision)
Display precision for floating-point numbers, i.e. the number of digits shown.
\P system command for detail
-q (quiet mode)
Quiet, i.e. no startup banner text or session prompts. Typically used where no console is required.
~/q$ q KDB+ 3.5t 2017.02.28 Copyright (C) 1993-2017 Kx Systems …
q)2+2 4 q)
~/q$ q -q
.z.q (quiet mode)
-s (secondary threads)
Number of secondary threads or processes available for parallel processing.
\s system command for detail
-S (random seed)
N as value of random seed.
-t (timer ticks)
Period in milliseconds between timer ticks. Default is 0, for no timer.
\t system command for detail
Timeout in seconds for client queries, i.e. maximum time a client call will execute. Default is 0, for no timeout.
\T system command for detail
-u (disable syscmds)
-u (usr-pwd local)
-u 1 / blocks system functions and file access -U file / sets password file, blocks \x -u file / both the above
-u 1 disables
- system commands from a remote (signals
'access), including exit via
- access to files outside the current directory for any handle context (
.z.w) other than 0
Only a simple protection against “wrong” queries
For example, setting a system command in
.z.ts and starting the timer still works. The right system command could for example expose a terminal, so the user running the database could be fully impersonated and compromised from then on.
- sets a password file
\x(even on the local console)
The password file is a text file with one credential on each line. (No trailing blank line/s.)
The password can be
- plain text
- an MD5 hash of the password
- an SHA-1 hash of the password (since V4.0 2020.03.17)
q)raze string md5 "this is my password" "210d53992dff432ec1b1a9698af9da16" q)raze string -33!"mypassword" / -33! calculates sha1 "91dfd9ddb4198affc5c194cd8ce6d338fde470e2"
-u file combines the above, i.e.
-u file is equivalent to
-u 1 -U file.
Workspace limit in MB for the heap per thread. Default is 0: no limit.
Domain-local Since V4.0 2020.03.17 this command is no longer thread-local, but memory domain-local: it sets the limit for domain 0.
Other ways to limit resources
On Linux systems, administrators might prefer cgroups as a way of limiting resources.
On Unix systems, memory usage can be constrained using
limits virtual address space to 256MB.
$ ulimit -v 262144
-W (start week)
Set the start-of-week offset, where 0 is Saturday. The default is 2, i.e Monday.
\W system command for detail
-z (date format)
Set the format for
"D"$ date parsing: 0 for mm/dd/yyyy and 1 for dd/mm/yyyy.