knitr에서 readOGR 메시지 억제

.NET readOGR에서 오류 메시지 를 억제하는 방법이 궁금합니다 knitr. 내 MWE는 다음과 같습니다.

\documentclass{article} 
\begin{document}
<< Test >>=
library(rgdal)
dsn <- system.file("vectors", package = "rgdal")[1]
setwd(dsn)
cities <- readOGR(dsn=dsn, layer="cities")
@ 
\end{document}

이 함수 readOGR는 다음과 같은 메시지를 제공합니다.

OGR data source with driver: ESRI Shapefile 
Source: "/home/asd/R/i686-pc-linux-gnu-library/3.2/rgdal/vectors", layer: "cities"
with 606 features
It has 4 fields

그러나 나는이 메시지를 억제하고 싶다. 시도 message=FALSE했지만 작동하지 않았습니다.

수정 됨

sessionInfo()
R version 3.2.1 (2015-06-18)
Platform: i686-pc-linux-gnu (32-bit)
Running under: Ubuntu 14.04.2 LTS

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] grid      tools     stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] ggmap_2.4       mapproj_1.2-2   maps_2.3-9      leaflet_1.0.0   rgeos_0.3-11    rgdal_1.0-4    
 [7] maptools_0.8-36 sp_1.1-1        Hmisc_3.16-0    Formula_1.2-1   survival_2.38-2 lattice_0.20-31
[13] psych_1.5.4     ggbiplot_0.55   plyr_1.8.3      gplots_2.17.0   rsm_2.7-2       scales_0.2.5   
[19] ggplot2_1.0.1   xtable_1.7-4    highr_0.5       knitr_1.10.12   brew_1.0-6      stringr_1.0.0  

loaded via a namespace (and not attached):
 [1] RColorBrewer_1.1-2   jsonlite_0.9.16      reshape2_1.4.1       cluster_2.0.2        rstudioapi_0.3.1    
 [6] magrittr_1.5         acepack_1.3-3.3      gtable_0.1.2         htmltools_0.2.6      splines_3.2.1       
[11] dplyr_0.4.2          KernSmooth_2.23-14   htmlwidgets_0.5      gridExtra_0.9.1      R6_2.0.1            
[16] digest_0.6.8         colorspace_1.2-6     proto_0.3-10         stringi_0.5-2        yaml_2.1.13         
[21] lazyeval_0.1.10.9000 evaluate_0.7         labeling_0.3         RJSONIO_1.3-0        gdata_2.16.1        
[26] rpart_4.1-9          munsell_0.4.2        DBI_0.3.1            Rcpp_0.11.6          RgoogleMaps_1.2.0.7 
[31] png_0.1-7            MASS_7.3-41          parallel_3.2.1       assertthat_0.1       rjson_0.2.15        
[36] caTools_1.17.1       gtools_3.5.0         jpeg_0.1-8           latticeExtra_0.6-26  foreign_0.8-63      
[41] bitops_1.0-6         nnet_7.3-9           geosphere_1.3-13     formatR_1.2          mnormt_1.5-3